Fix prepare_commits_for_rendering N+1 spec

What does this MR do and why?

This MR fixes #344956 (closed) (spec/controllers/concerns/renders_commits_spec.rb:61) when it's executed for the first time. Subsequent runs pass because the Banzai::Filter::References::ReferenceCache is populated. This MR ensures that this cache is always populated before we execute prepare_commits_for_rendering against the entire array.

Failures:
  1) RendersCommits.prepare_commits_for_rendering avoids N+1
     Failure/Error:
       expect do
         subject.prepare_commits_for_rendering(merge_request.commits)
         merge_request.commits.each(&:latest_pipeline)
       end.not_to exceed_all_query_limit(control.count)
       Expected a maximum of 5 queries, got 12:
     # ........................................
     # ........................................
     # ........................................
     # ./spec/controllers/concerns/renders_commits_spec.rb:67:in `block (3 levels) in <top (required)>'
     # ./spec/spec_helper.rb:416:in `block (3 levels) in <top (required)>'
     # ./spec/support/sidekiq_middleware.rb:9:in `with_sidekiq_server_middleware'
     # ./spec/spec_helper.rb:407:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:403:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/application_context.rb:31:in `with_raw_context'
     # ./spec/spec_helper.rb:403:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:207:in `block (2 levels) in <top (required)>'
     # ./spec/support/database/prevent_cross_joins.rb:102:in `block (3 levels) in <top (required)>'
     # ./spec/support/database/prevent_cross_joins.rb:56:in `with_cross_joins_prevented'
     # ./spec/support/database/prevent_cross_joins.rb:102:in `block (2 levels) in <top (required)>'

Click to see extra queries

D, [2021-11-08T14:50:43.109890 #1826866] DEBUG -- :   MergeRequest Load (0.4ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 11 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.110229 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.141571 #1826866] DEBUG -- :   MergeRequest Load (0.4ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 10 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.141882 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.190876 #1826866] DEBUG -- :   MergeRequest Load (0.3ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 9 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.191162 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.234905 #1826866] DEBUG -- :   MergeRequest Load (0.4ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 6 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.235238 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.278617 #1826866] DEBUG -- :   MergeRequest Load (0.4ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 5 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.278951 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.310215 #1826866] DEBUG -- :   MergeRequest Load (0.4ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 4 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.310536 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.372556 #1826866] DEBUG -- :   MergeRequest Load (0.4ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 3 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.372934 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'
D, [2021-11-08T14:50:43.469862 #1826866] DEBUG -- :   MergeRequest Load (0.3ms)  SELECT "merge_requests".* FROM "merge_requests" WHERE "merge_requests"."target_project_id" = 22 AND "merge_requests"."iid" = 2 /*application:test,correlation_id:93c8c95cfeebef9ebc96637aef15cd0c,db_config_name:main*/
D, [2021-11-08T14:50:43.470182 #1826866] DEBUG -- :   ↳ lib/banzai/filter/references/reference_cache.rb:90:in `block in load_records_per_parent'

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Execute this command on master

   gdk restart && bin/rspec spec/controllers/concerns/renders_commits_spec.rb:61

2. Ensure that it fails

3. Execute it after checking out to this MR branch

   gdk restart && bin/rspec spec/controllers/concerns/renders_commits_spec.rb:61

4. Ensure that now it succeeds

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #344956 (closed)