pw-pull: Propagate tags onto pull requests

Some reviewers review pull requests and should be rewarded
for it. Since we can't change the commits try to at least
propagate the tags sent in response to the PR or cover letter.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>