Master broken 6617 fix flaky vulnerability finder presenter

What does this MR do and why?

Fixes flaky test.

1) Vulnerabilities::FindingPresenter#blob_path without a sha is expected to be blank
     Failure/Error: it { is_expected.to be_blank }
       expected `"/namespace1/project-1/-/blob/master/a.txt#L1-2".blank?` to be truthy, got false
     # ./ee/spec/presenters/vulnerabilities/finding_presenter_spec.rb:50:in `block (4 levels) in <main>'
     # ./spec/spec_helper.rb:448:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/sidekiq_sharding/validator.rb:42:in `enabled'
     # ./spec/spec_helper.rb:447:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:442:in `block (3 levels) in <top (required)>'
     # ./spec/support/sidekiq_middleware.rb:9:in `with_sidekiq_server_middleware'
     # ./spec/spec_helper.rb:433:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:429:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/application_context.rb:70:in `with_raw_context'
     # ./spec/spec_helper.rb:429:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:261:in `block (2 levels) in <top (required)>'
     # ./spec/support/system_exit_detected.rb:7:in `block (2 levels) in <main>'
     # ./spec/support/fast_quarantine.rb:22:in `block (2 levels) in <main>'
     # ./spec/support/database/prevent_cross_joins.rb:106:in `block (3 levels) in <main>'
     # ./spec/support/database/prevent_cross_joins.rb:60:in `with_cross_joins_prevented'
     # ./spec/support/database/prevent_cross_joins.rb:106:in `block (2 levels) in <main>'

Finished in 57.58 seconds (files took 56.72 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./ee/spec/presenters/vulnerabilities/finding_presenter_spec.rb:50 # Vulnerabilities::FindingPresenter#blob_path without a sha is expected to be blank

See: gitlab-org/quality/engineering-productivity/master-broken-incidents#6617 (comment 1924134495)

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