Add CI step help debug what the diff is

Author: simonbaird

.github/workflows/checks-codecov.yaml

@@ -79,6 +79,11 @@ jobs:
             exit 1
           fi
 
+      # Debugging what the actual diff is
+      - name: Show the diff
+        run: |
+          git diff --stat --patch
+
       - name: Test
         run: make test