The runner only references `GitInfoCommitHash`/`CommitHash` to print
informational log entries. To allow for just referencing the tag of a
version instead of the commit hash, this commit sets the value of the
`GitInfoCommitHash` to a static dummy value.

As of yet, a patch caused the runner to discard update messages.
Unfortunately, GitHub keeps sending update messages to outdated runners
causing them to no longer pick up jobs.

This commit causes the runner to send a high version to GitHub which
should be more recent for quite a time. That way, GitHub does not send
update message and keeps scheduling jobs even for outdated runners.

Naturally, an oudated runner can still break at any time as GitHub's
current approach assumes that all runners are always up-to-date. We
should still strive for quick nixpkgs updates but this patch should give
us some time.