Modern versions of git will return progress information. In debugging what goes on here, I found that all of the information was being dropped by _parse_line. For others who run into this, I was able to return branch update information to the user by adding the following:

classSeeFetchProgress(git.remote.RemoteProgress):# the implementation of RemoteProgress currently doesn't match fetch lines, so catch them when dropped.defline_dropped(self,line:str):ifre.match('remote: ',line):returnprint(line)