follow symrefs when pushing

When pushing to a plain Git URL, it's very common to get an error that looks something like this:

git: refusing to create funny ref 'HEAD' remotely
brz: ERROR: Unable to update remote HEAD branch. To update the master branch, specify the URL git+ssh://<email address hidden>/jelmer/blah,branch=master.

It's possible to avoid this by following symrefs during push on servers that support it (which includes GitHub).