Update GitHub actions to the latest versions

[RealTriassic]

As Node.js 16 actions are deprecated according to GitHub, I have updated all of the GitHub actions to their latest versions. I also went ahead and enabled caching to shave off about half a minute of build time, not sure if you want this, but let me know if not.

I also removed an unnecessary build step. You do not need to manually make gradlew executable, it already is.