fleximod_test.yaml: Show the diffs again

Author: samsrabin

.github/workflows/fleximod_test.yaml

@@ -26,7 +26,7 @@ jobs:
           echo
           echo "Checking if git fleximod matches expected externals"
           echo
-          git add . && git diff --quiet && git diff --cached --quiet
+          git add . && git diff --exit-code && git diff --cached --exit-code
 #      - name: Setup tmate session
 #        if: ${{ failure() }}
 #        uses: mxschmitt/action-tmate@v3