Most of our GitHub Actions have started failing recently with:

FAILURE: Build failed with an exception.

What went wrong:
Execution failed for task ':admob:app:validateSigningDebug'.
java.io.IOException: Unable to create debug keystore in /home/runner/.config/.android because it is not writable.
138 actionable tasks: 86 executed, 13 from cache, 39 up-to-date

Try:
Run with --stacktrace option to get the stack trace.
Run with --info or --debug option to get more log output.
Run with --scan to get full insights.
Get more help at https://help.gradle.org.

BUILD FAILED in 3m 46s
Error: Process completed with exit code 1.

Not entirely sure why, but I'm guessing something changed in GitHub Actions recently.