Merge branch '55402-broken-master-karma-test-failing-in-spec-javascripts-boards-components-issue_due_date_spec-js' into 'master'

Resolve "Broken master: karma test failing in spec/javascripts/boards/components/issue_due_date_spec.js"

Closes #55402

See merge request gitlab-org/gitlab-ce!23845

Fixed upload file button not working for repo cleanup

See merge request gitlab-org/gitlab-ee!8858

Display empty files properly on MR diffs

Closes #54786

See merge request gitlab-org/gitlab-ce!23671

Resolve transient failure in Help page spec

Closes #55372

See merge request gitlab-org/gitlab-ce!23839

Resolve "Merge button does not appear after Rebase-ing"

Closes #47052

See merge request gitlab-org/gitlab-ce!23572

Set cached MRWidget SHA after rebase

See merge request gitlab-org/gitlab-ee!8847

Fixed link in doc/ci/yaml/README.md

See merge request gitlab-org/gitlab-ce!23433

Refactor the only and except complex section

See merge request gitlab-org/gitlab-ce!23792

Docs: Let's Encrypt certificate for GitLab Pages

Closes #51979

See merge request gitlab-org/gitlab-ce!23777

Refactor the only and except complex section

See merge request gitlab-org/gitlab-ee!8837

Remove "Switching to Rails 5" documentation

See merge request gitlab-org/gitlab-ee!8867

EE port of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23840

Removed rails 5 documentation

See merge request gitlab-org/gitlab-ce!23840

Remove Rails 4 support

See merge request gitlab-org/gitlab-ce!23717

Resolve a transient failure in MWPS feature spec

Closes gitlab-ee#6770

See merge request gitlab-org/gitlab-ce!23838

Sometimes due to a slow request to load the version check image, the
placeholder image data was still being seen, resulting in this failure:

    expected "data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==" to end with "/version-check-url"

Now we check the `data-src` attribute, which allows us to remove the
`:js` metadata.

This commit also removes a redundant test, which was just ensuring that
the selector we were already using in the other test is visible. If this
test were failing, the other one would always fail too, so it was
pointless.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/55372

All of these methods are stateless, there was no point to have them as
instance methods.

Mostly this allows us to remove an `allow_any_instance_of` usage.

Remove Rails 4 support

Closes #8761

See merge request gitlab-org/gitlab-ee!8781

Because we removed rails 4 support, this document is not needed
anymore.

Remove CREATE_DB_USER variable in prepare_build

See merge request gitlab-org/gitlab-ce!23815

Update prettier.md with VSCode Settings section

See merge request gitlab-org/gitlab-ce!23810

https://gitlab.com/gitlab-org/gitlab-ce/issues/55230#note_124977178

When this spec is run in a certain order, there appeared to be a timing
issue with opening the "Merge when pipeline succeeds" drop-down menu. We
now explicitly wait for any pending requests to complete before clicking
the drop-down.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/6770

Fix the database schema

See merge request gitlab-org/gitlab-ee!8864

Fix warnings in tests

See merge request gitlab-org/gitlab-ce!23788

Refactor Ci::Pipeline's config_sources enum

Closes gitlab-ee#8244

See merge request gitlab-org/gitlab-ce!23799