[WIP] CI Improvements

[add-apt-repository]

Please ensure that your pull request meets the following requirements - thanks!

• Does not contain merge commits. Rebase instead.
• Contains commits with descriptive titles.
• New code is written in Kotlin whenever possible.
• Follows our existing codestyle (gradlew spotlessCheck to check and gradlew spotlessApply to format your source code; will be checked by CI).
• Does not break any unit tests (gradlew testDebugUnitTest; will be checked by CI).
• Uses a descriptive title; don't put issue numbers in there.
• Contains a reference to the issue that it fixes (e.g. Closes #XXX or Fixes #XXX) in the body text.
• For cosmetic changes add one or multiple images, if possible.

Finally, please replace this template text with a description of the change and additional context if necessary.