The old Travis CI .org service has been throttled for a while now and is
said to be shutting down completely next week.
This migrates the Travis CI build jobs to GitHub Actions, with minor
changes.
- The trailing whitespace detection has been removed for now.
- The libegl1-mesa-dev dependency for Wayland has been removed as it
appears to no longer be necessary for building.
(cherry picked from commit 5a6001a83b)
