Fix run_after_commit_or_now to use model's connection

What does this MR do and why?

Fix run_after_commit_or_now to use model's connection

Related issue: #346309 (closed)

Screenshots or screen recordings

Before the application changes:

$ GITLAB_USE_MODEL_LOAD_BALANCING=1 bin/rspec spec/models/concerns/after_commit_queue_spec.rb 
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Test environment set up in 6.592182 seconds
.....F

Failures:

  1) AfterCommitQueue#run_after_commit_or_now multiple databases - Ci::ApplicationRecord models runs after transaction has completed
     Failure/Error: expect(called).to be false
     
       expected false
            got true
     # ./spec/models/concerns/after_commit_queue_spec.rb:121:in `block (5 levels) in <top (required)>'
     # ./lib/gitlab/database/load_balancing/connection_proxy.rb:126:in `block in write_using_load_balancer'
     # ./lib/gitlab/database/load_balancing/load_balancer.rb:112:in `block in read_write'
     # ./lib/gitlab/database/load_balancing/load_balancer.rb:172:in `retry_with_backoff'
     # ./lib/gitlab/database/load_balancing/load_balancer.rb:110:in `read_write'
     # ./lib/gitlab/database/load_balancing/connection_proxy.rb:125:in `write_using_load_balancer'
     # ./lib/gitlab/database/load_balancing/connection_proxy.rb:77:in `transaction'
     # ./lib/gitlab/database.rb:261:in `block in transaction'
     # ./lib/gitlab/database.rb:260:in `transaction'
     # ./spec/models/concerns/after_commit_queue_spec.rb:112:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:412:in `block (3 levels) in <top (required)>'
     # ./spec/support/sidekiq_middleware.rb:9:in `with_sidekiq_server_middleware'
     # ./spec/spec_helper.rb:403:in `block (2 levels) in <top (required)>'
     # ./spec/spec_helper.rb:399:in `block (3 levels) in <top (required)>'
     # ./lib/gitlab/application_context.rb:31:in `with_raw_context'
     # ./spec/spec_helper.rb:399:in `block (2 levels) in <top (required)>'
     # ./spec/support/database/query_analyzer.rb:9:in `block (3 levels) in <main>'
     # ./lib/gitlab/database/query_analyzer.rb:42:in `within'
     # ./spec/support/database/query_analyzer.rb:9: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 10.89 seconds (files took 10.47 seconds to load)
6 examples, 1 failure

Failed examples:

rspec ./spec/models/concerns/after_commit_queue_spec.rb:108 # AfterCommitQueue#run_after_commit_or_now multiple databases - Ci::ApplicationRecord models runs after transaction has completed

After:

$ GITLAB_USE_MODEL_LOAD_BALANCING=1 bin/rspec spec/models/concerns/after_commit_queue_spec.rb
Run options: include {:focus=>true}

All examples were filtered out; ignoring {:focus=>true}

Test environment set up in 6.623249 seconds
......

Finished in 10.78 seconds (files took 10.65 seconds to load)
6 examples, 0 failures

How to set up and validate locally

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

MR acceptance checklist

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