Cleanup CI, test meson dist

[danirod]

Given that the release process now requires manual action (due to app signing) instead of just accepting whatever generates Github Actions, I could cleanup the actions to remove the duplicity between the nightly and stable actions.

• No more nightly / stable.

  • Remove stable jobs.
  • Nightly jobs are now just "build" (or "test-build").

• Should run meson dist, reasons:

  • It does some linting so it is worth testing that it works OK.
  • The release process now uses meson dist because I build the releases from the tarball, so it's worth using it.
  • Maybe I can save some time during compilation if I use the output of meson dist in order to clippy and test-build.