fix: errors with anonymous user (#29042)

There are several errors that appear in monitoring when calls
are made with an anonymous user. This resolves one (or more).

openedx/core/djangoapps/user_api/course_tag/api.py

@@ -69,6 +69,9 @@ def get_course_tag(user, course_id, key):
     Returns:
         string value, or None if there is no value saved
     """
+    if user.is_anonymous:
+        return None
+
     if BulkCourseTags.is_prefetched(course_id):
         try:
             return BulkCourseTags.get_course_tag(user.id, course_id, key)

openedx/core/djangoapps/user_api/course_tag/tests/test_api.py

@@ -2,7 +2,7 @@
 Test the user course tag API.
 """
 
-
+from django.contrib.auth.models import AnonymousUser
 from django.test import TestCase
 from opaque_keys.edx.locator import CourseLocator
 
@@ -21,6 +21,10 @@ class TestCourseTagAPI(TestCase):
         self.course_id = CourseLocator('test_org', 'test_course_number', 'test_run')
         self.test_key = 'test_key'
 
+    def test_get_course_tag_for_anonymous_user(self):
+        tag = course_tag_api.get_course_tag(AnonymousUser(), self.course_id, self.test_key)
+        assert tag is None
+
     def test_get_set_course_tag(self):
         # get a tag that doesn't exist
         tag = course_tag_api.get_course_tag(self.user, self.course_id, self.test_key)