Suppress locale.getdefaultlocale warning in project template test

It comes from l18n

.github/workflows/test.yml

@@ -160,9 +160,13 @@ jobs:
         run: |
           wagtail start testproject
           cd testproject
-          # Remove when all experimental jobs use Django >= 6.0
           tee -a testproject/settings/local.py << EOF
           from warnings import filterwarnings
+          # Remove when l18n dependency is updated or removed
+          filterwarnings(
+              "ignore", "'locale.getdefaultlocale' is deprecated .*"
+          )
+          # Remove when all experimental jobs use Django >= 6.0
           filterwarnings(
               "ignore", "The FORMS_URLFIELD_ASSUME_HTTPS transitional setting is deprecated."
           )