fix(test_docs): skip master-dependent assertion
fix(test_docs): skip master-dependent assertion

It usually fails on branches, which doesn't help
assessing PRs.

nvie/GitPython,breavo/GitPython,jeblair/GitPython,nvie/GitPython,gitpython-developers/GitPython,jeblair/GitPython,gitpython-developers/GitPython,breavo/GitPython,expobrain/GitPython,expobrain/GitPython,gitpython-developers/gitpython,gitpython-developers/gitpython