Fixes concurrency group to speed up merge queues

[koppor]

This PR enables parallel builds in the merge queue. Now, merges are build in parallel, but with the previous entries in the merge queue inside. In case a predecessor fails, it is exluded and the all subsquent builds are run again. See https://github.com/orgs/community/discussions/63136#discussioncomment-7738973 for a graphics.

I tried out the "fix" at https://github.com/winery/test-concurrency-at-merge-queues - and it looked good! 😅

More background: After thinking more of https://github.com/orgs/community/discussions/63136 and why GitHub did not answer it, I thought, it must be a user error.

Mandatory checks

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

If it works, we need to report at https://github.com/orgs/community/discussions/63136

[github-actions]

The build for this PR is no longer available. Please visit https://builds.jabref.org/main/ for the latest build.

[koppor]

Queue while building:

Queued PR:

[koppor]

Queue waits for others being added:

---

For each build, another branch is created

github.ref

The fully-formed ref of the branch or tag that triggered the workflow run. For workflows triggered by push, this is the branch or tag ref that was pushed. For workflows triggered by pull_request, this is the pull request merge branch. For workflows triggered by release, this is the release tag created. For other triggers, this is the branch or tag ref that triggered the workflow run. This is only set if a branch or tag is available for the event type. The ref given is fully-formed, meaning that for branches the format is refs/heads/<branch_name>, for pull requests it is refs/pull/<pr_number>/merge, and for tags it is refs/tags/<tag_name>. For example, refs/heads/feature-branch-1.

Source: https://docs.github.com/en/actions/learn-github-actions/contexts

github.head_ref:

The head_ref or source branch of the pull request in a workflow run. This property is only available when the event that triggers a workflow run is either pull_request or pull_request_target.

Source: https://docs.github.com/en/actions/learn-github-actions/contexts

[koppor]

I tested it again. Works (in the little scenario)

Will merge in and adapt merge queue settings.

Let's see, what happens :p