Run python linter on contrib directory, excluding only gitian_updater which is third-party code.
For mypy exclude also macdeploy, because there are some non-trivial errors that will take more work to be fixed.
For lint-python-encoding, skip a file that has a open(filename, self.mode) false positive. This linter seems a bit too restrictive, but as long as there is only a single false positive it is easiest to just ignore it.
This is a backport of core#20451