Upgrade mail and nokogiri gems due to security issues

See merge request !13662

[ci skip]

Improve migrations / background migrations testing strategy

Closes #36303

See merge request !13589

This reverts commit 775cee73.

Clear schema cache after running tests for migrations

Closes #37086

See merge request !13870

This reverts commit 6d6223ec, reversing
changes made to cc781170.

Instrument MergeRequest#fetch_ref

See merge request !13980

Fixes the fly-out navigation flashing in & out

Closes #37022

See merge request !13929

Rollback changes made to signing_enabled.

Closes #37202

See merge request !13956

Remove closing external issues by reference error

Closes #36820

See merge request !13910

Update translation for zh-TW to remove percents

See merge request !13988

Fix "Merge when pipeline succeeds" button dropdown caret icon horizontal alignment

Closes #37194

See merge request !13965

Merge branch 'pawel/bump_prometheus_client_mmap_version_to_fix_performance_degradation' into 'master'

Update Prometheus Client MMAP gem to version that fixes performance degradation

See merge request !13898

Remove skipped examples in filtered issues feature spec

See merge request !13845

Update Gitaly version to v0.35.0

Closes #36972 and gitaly#486

See merge request !13950

Fix events error importing GitLab projects

Closes #36965

See merge request !13868

Filter additional parameters that have shown up in our logs

See merge request !13945

Removes disabled state from projects dropdown in dashboard page

Closes #37179

See merge request !13933

Fixed fly-out nav jumping

Closes #36699

See merge request !13690

Resolve "README.md: Header image scale not limited"

Closes #37058, #37024, and #37230

See merge request !13869

Increase z-index of dropdowns

Closes #36766 and #36866

See merge request !13889

Update backup_restore.md documentation regarding S3 and IAM profiles.

See merge request !13871

Eager load head pipeline projects for MRs index

See merge request !13877

Adds position fixed to right sidebar

Closes #37144

See merge request !13494

Fixes the diff changes buttons from toggling when scrolling

Closes #36698

See merge request !13894

Make username update fail if namespace update fails

Closes gitlab-com/support-forum#2316

See merge request !13642

fix transient dropdown test failures

Closes #37052 and #34436

See merge request !13862

Merge branch 'fix/sm/37040-regression-pipeline-trigger-via-api-fails-with-500-internal-server-error-in-9-5-1' into 'master'

Fix pipeline trigger via API fails with 500 Internal Server Error in 9.5.1

Closes #37040

See merge request !13861

Refactor Gitlab::Git::Commit to include a repository and add missing specs

See merge request !13815

Add dynamic navigation tunnel to fly-out menus

Closes #35949

See merge request !13315

Optimize notification emails specs

See merge request !13986

Update and fix resolvable note icons for easier recognition

Closes #36582

See merge request !13821

Update templates to include header in the README

Closes #36904

See merge request !13785

Improve flaky ACE editor spec

See merge request !13854

Instrument MergeRequest#ensure_ref_fetched

See merge request !13876

Simplify system hook testing and guarantee test will fire

Closes #37067

See merge request !13858

Bugfix.notify custom participants

Closes #36610

See merge request !13680