Cirrus-CI: Use the default Git history depth

Which is 50. I saw a few errors like
Failed to force reset to SHA: object not found! which seems is
happening because the SHA is not available because there were two
commits pushed almost simultaneously and the second from the top fails
with this error because the SHA is not in the history.

Pull Request: https://github.com/freebsd/freebsd-src/pull/454