Merge branch 'renovate/python-gitlab-3.x' into 'main'

Update dependency python-gitlab to v3.15.0

See merge request !55

requirements.in

 prometheus-client==0.17.0
 python-dateutil==2.8.2
-python-gitlab==3.14.0
+python-gitlab==3.15.0
 requests==2.31.0
 # Needed for renovatebot
 pip-tools==6.13.0

requirements.txt

@@ -24,7 +24,7 @@ pyproject-hooks==1.0.0
     # via build
 python-dateutil==2.8.2
     # via -r requirements.in
-python-gitlab==3.14.0
+python-gitlab==3.15.0
     # via -r requirements.in
 requests==2.31.0
     # via