Ignore import warnings from gobject-introspection.

This is an incompatibility with Python 3.10 that is not fixed there yet.
https://gitlab.gnome.org/GNOME/pygobject/-/issues/473

Author: QuLogic

lib/matplotlib/testing/conftest.py

@@ -21,6 +21,9 @@ def pytest_configure(config):
         ("filterwarnings", "error"),
         ("filterwarnings",
          "ignore:.*The py23 module has been deprecated:DeprecationWarning"),
+        ("filterwarnings",
+         r"ignore:DynamicImporter.find_spec\(\) not found; "
+         r"falling back to find_module\(\):ImportWarning"),
     ]:
         config.addinivalue_line(key, value)