Add CI to test compilation

[kurtmckee]

I noticed that xone doesn't have CI. This PR introduces the following changes:

• Add CI to test compilation of the project.

  GitHub runners don't have a soundsystem, so generic kernel headers are installed and compiled against.

• Add a Dependabot config that will submit a PR every six months to update the actions/checkout version.

You can see an example of a successful CI run in my fork. Also, more could be done to lint and test the project, including:

• Running shellcheck to confirm that the *.sh scripts follow best practices
• Running clang-format to confirm that the code is formatted correctly
• Running zizmor to confirm that the GitHub workflow continues to follow best practices for security (I ran zizmor in pedantic mode against the workflow in this PR to confirm that there are no known security issues)

I can add more in subsequent PRs if you'd like, but this at least confirms that the code compiles when you receive PRs from contributors.

Thanks for your work on xone!