title: Gitpython git push does not raise exception when failing to push
body: <p>This seems to be a known issue, however I'm looking for a workaround. Anyone know of a good workaround?</p>
  <p><a href="https://github.com/gitpython-developers/GitPython/issues/621" rel="nofollow noreferrer">https://github.com/gitpython-developers/GitPython/issues/621</a></p>
  <pre><code>(Pdb) test = self.repo.remotes.origin.push(refspec=self.base_branch, progress=None, force=False)
  2020-07-18 12:06:55,744|WARNING|guest|Error lines received while fetching: error: failed to push some refs to 'git@github.com:test/test.git'
  hint: Updates were rejected because the remote contains work that you do
  hint: not have locally. This is usually caused by another repository pushing
  hint: to the same ref. You may want to first integrate the remote changes
  hint: (e.g., 'git pull ...') before pushing again.
  hint: See the 'Note about fast-forwards' in 'git push --help' for details.
  (Pdb)```
  </code></pre>