Pick for 9.5: "Refactor how we fetch ref for merge requests"

See merge request !14213

Refactor how we fetch ref for merge requests

Closes #36089 and #36296

See merge request !13416

alternative is to pick !13872

changed in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13984/

Use rspec-parameterized for table-based tests

Closes #35804

See merge request !13469

This reverts commit dd406182, reversing
changes made to d5d24976.

GPG signature must match the committer in order to be verified

See merge request !13771

Perf.slow issuable

Closes #32844

See merge request !13685

Only update the sidebar count caches when needed

See merge request !13878

Improve migrations using triggers

Closes #36633

See merge request !13666

Fix new_sidebar.scss being out of date

See merge request !14035

Fix new navigation wrapping caret and increasing height

Closes #36821

See merge request !13967

Fix buttons with different height in merge request widget

Closes #37331

See merge request !14000

Increase the timeout before aborting a storage access attempt

See merge request !14023

Creates an icon only for the discussions and puts back the old SVG for CI status

Closes #37406

See merge request !14042

Fix problems sanitizing URLs with empty passwords

Closes gitlab-ee#3352

See merge request !14083

Fix a wrong `X-Gitlab-Event` header when testing webhooks

Closes #37288

See merge request !14108

Update docs for confidential issues

Closes #36352

See merge request !14117

Hide group title on sidebar collapse; use more generic class for titles

Closes #36589

See merge request !13777

Disable GitLab Project Import Button if source disabled

Closes #36882

See merge request !13789

Fix division by zero for blame age map

Closes #35441

See merge request !13803

Merge branch '36638-select-project-to-create-issue-button-is-disconnected-from-dropdown-button' into 'master'

Normalize styles for empty-state group-level new issue/MR combo button

Closes #36638

See merge request !13647

[ci skip]

Upgrade mail and nokogiri gems due to security issues

See merge request !13662

Upgrade mail and nokogiri gems due to security issues

See merge request !13662

Fix Live Comment XSS Vulnerability

See merge request gitlab/gitlabhq!2183

Merge 9-5-stable into security-9-5

See merge request gitlab/gitlabhq!2184

[9.5] Prevent a persistent XSS in the commit author block

See merge request gitlab/gitlabhq!2180

[ci skip]

Improve migrations / background migrations testing strategy

Closes #36303

See merge request !13589

This reverts commit 775cee73.