github: investigate merge queues

[matzf]

We currently use the setting "Require branches to be up to date before merging":

This ensures pull requests targeting a matching branch have been tested with the latest code. This setting will not take effect unless at least one status check is enabled.

This is good because it ensures that commits in master always pass the status checks, i.e. CI runs. However, it makes it somewhat cumbersome and slow to merge multiple PRs in sequence, as the branches need to be updated manually and the CI checks occur entirely sequentially.

Github has a feature called "Merge Queue", that essentially automate this process. See https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue

Investigate if this can be used with our workflows and the integrated tools, i.e.

• buildkite
• readthedocs
• reviewable
• viper/gobra code verification

[matzf]

Update: reviewable now supports merge queues explicitly (https://changelog.reviewable.io/changelog-june-273797)