Add composer diagnose to check github rate limiting

Author: leith

.github/workflows/phpunit.yml

@@ -44,6 +44,9 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
+      - name: "Composer diagnostics"
+        run: "composer diagnose"
+
       - name: "Install lowest dependencies"
         if: ${{ matrix.dependencies == 'lowest' }}
         run: "composer update --prefer-lowest --no-interaction --no-progress"