GitHub Actions CI Build Improvements

[stevenzeck]

This PR aims to improve the build times in GitHub Actions, as they are taking 20+ minutes now.

1. Enabled parallel builds of the individual modules.
2. Removed clean from the task, as it's not needed.
3. Cache gradle dependencies.
4. Combine build and test steps.
5. Remove building any release variants.

[mickael-menu]

Weirdly, it seems to be taking more time now 😅 I restarted the build to make sure it used the Gradle cache but it didn't seem to change anything.

[stevenzeck]

It won't cache anything until it goes into main or develop, per cache-read-only: ${{ github.ref != 'refs/heads/main' && github.ref != 'refs/heads/develop' }}. But I also changed the workflow steps to combine build and test, and only build the debug variant and not release. Looks much better, and will improve once things are cached.

And I think it ran low on memory with parallelization at 4 GB.

[mickael-menu]

Thank you @stevenzeck, this is a nice improvement!