Update dependency gitpython to v3.1.26

Author: renovate-bot

requirements.txt

@@ -10,7 +10,7 @@ django==4.0.1
     # via django-migration-fixer (setup.py)
 gitdb==4.0.9
     # via gitpython
-gitpython==3.1.25
+gitpython==3.1.26
     # via django-migration-fixer (setup.py)
 pytz==2021.3
     # via django