Set the diff-compare branch to main

Signed-off-by: Patrick Uiterwijk <[email protected]>

.github/workflows/ci.yml

@@ -46,7 +46,7 @@ jobs:
     - name: Ensure test coverage
       run: |
         coverage xml
-        diff-cover coverage.xml --fail-under=100
+        diff-cover coverage.xml --fail-under=100 --compare-branch main
     - name: Ensure code quality change
       run: |
         diff-quality --violations=flake8 --fail-under=100