Fix brittle spec for hooks

What does this MR do and why?

Related to !93665 (merged)

Problem

If run the test suite for bundle exec rspec --format documentation gitlab/spec/services/git/branch_push_service_spec.rb separately it fails:

1) Git::BranchPushService Webhooks when pushing a branch for the first time executes webhooks
     Failure/Error: expect(project).to receive(:execute_hooks)

       (#<Project id:45 namespace1/project1>>).execute_hooks(*(any args))
           expected: 1 time with any arguments
           received: 0 times with any arguments
     # ./spec/services/git/branch_push_service_spec.rb:205:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:432:in `block (3 levels) in <top (required)>'
     # ./spec/support/sidekiq_middleware.rb:9:in `with_sidekiq_server_middleware'
     # ./spec/spec_helper.rb:423:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:419:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/application_context.rb:56:in `with_raw_context'
     # ./spec/spec_helper.rb:419:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:262:in `block (2 levels) in <top (required)>'
     # ./spec/support/system_exit_detected.rb:7: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>'

Solution

The project stores memoized values from the previous tests and we need to refind the project to fix it.

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