increased requested gitpython version to v3.0.8 to avoid this:

gen2 · gen2 · commit 66f26f02f18c · 2020-03-19T14:49:28.000+01:00
gitpython-developers/GitPython#983
diff --git a/requirements.txt b/requirements.txt
@@ -8,4 +8,4 @@ obspy==1.1.0
 python-dateutil==2.8.0
 pytest==5.0.1
 vcrpy==2.0.1
-gitpython==3.0.5
+gitpython==3.0.8
