Update Permissions-Policy to disable Topics

django-permissions-policy was added by #124 to disable Google's
[Federated Learning of
Cohorts](https://privacysandbox.com/proposals/floc/) (FLoC). FLoC was
replaced by [Topics](https://privacysandbox.com/proposals/topics/) in
May 2023, so we update the Permissions-Policy header to disable Topics.

actions/settings.py

@@ -219,6 +219,9 @@ def immutable_file_test(path, url):
 # https://github.com/adamchainz/django-permissions-policy/blob/main/README.rst
 PERMISSIONS_POLICY = {
     "interest-cohort": [],
+    # The following disables Google's Topics. For more information, see:
+    # https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Permissions-Policy/browsing-topics
+    "browsing-topics": [],
 }