Don't mark empty MRs as merged on push to the target branch

Closes #32800

See merge request !12711

Allow admins to retrieve user agent details for an issue or snippet

Closes #29508

See merge request !12655

Test logging in via the Authentiq OAuth provider in a feature spec

Closes #34737

See merge request !12694

Fixed text overflow issue in new sidebars

See merge request !12648

Moves alert boxes to below the breadcrumbs

See merge request !12631

Migrate Gitlab::Git::Repository#commit_count to Gitaly

Closes gitaly#355

See merge request !12688

Add variables to pipelines schedules

Closes #32568

See merge request !12372

Fix dashboard labels dropdown

Closes #34590

See merge request !12708

Native group milestones

See merge request !12280

Speed up `all_commit_shas` for new merge requests

See merge request !12706

Resolve "Inconsistent location of members page between groups and projects"

Closes #29893

See merge request !11560

N+1 problems on milestone page

Closes #34736

See merge request !12670

When we push to an MR's target branch, we check if the MR's HEAD commit is
contained in the push. This lets us mark MRs as merged if they were merged
manually.

However, we also added a feature where you can create an empty MR from an
issue. If that MR is created around the time of a merge to the default branch,
we would process the push after creating the MR, and consider it to be a manual
merge.

To fix that, we exclude empty MRs from this process. If they are empty, they
were empty before the push we're processing, so we shouldn't touch them!

This makes the `Boards::CreateService` more reusable for EE

See merge request !12704

Follow-up from "Namespace license checks for multiple assignees"

Closes gitlab-ee#2839

See merge request !12701

Refactor several javascript files to ES module syntax

See merge request !12683

Fix ShaAttribute concern when there is no table

Closes #34798

See merge request !12705

For merge requests created after 9.4, we have a `merge_request_diff_commits`
table we can get all the SHAs from very quickly. We just need to exclude these
when we load from the legacy format, by ignoring diffs with no serialised
commits.

Once these have been migrated in the background, every MR will see this
improvement.

Add Group secret variables

Closes #12729

See merge request !12582

Remove option to disable Gitaly in Rails

See merge request !12677

Closes gitaly#355

When this is added to a new model, it would fail before the migrations were run
- including when trying to run migrations in production mode!

Update VERSION to 9.4.0-pre.

See merge request !12702

Extend MR tabs a bit to cover up the avatar holder and collapse icon on scroll

Closes #34153

See merge request !12589