The cache-cleanup API has changed, so the init-script that worked with
Gradle 8.9 no longer works with 8.11.
We now provision and use Gradle 8.11 for cache cleanup.
This provides a band-aid fix for #417 but that issue will still impact
any build configured to run with Gradle > 8.11
Instead of relying on push triggers in general, we now use pull_request
and reserve push triggers for main and release branches.
This makes the behaviour more consistent for users contributing from
repository forks. However, we no longer have a quick-feedback loop
for development.
