pytest: Don't raise FutureWarning to Error

FutureWarning can stay a FutureWarning in the CI, it doesn't need to be raised to an Error (note it also isn't suppresed). Otherwise we can't use experimental features in examples.

.github/workflows/build_lint.yml

@@ -86,4 +86,4 @@ jobs:
     - name: Test examples
       run: |
         cd mesa-examples
-        pytest -rA -Werror test_examples.py
+        pytest -rA -Werror -Wdefault::FutureWarning test_examples.py