chore: Replace pytz with zoneinfo for UTC handling - Part 1 (#37523)

First PR to replace pytz with zoneinfo for UTC handling across codebase.

This PR migrates all UTC timezone handling from pytz to Python’s standard
library zoneinfo. The pytz library is now deprecated, and its documentation
recommends using zoneinfo for all new code. This update modernizes our
codebase, removes legacy pytz usage, and ensures compatibility with
current best practices for timezone management in Python 3.9+. No functional
changes to timezone logic - just a direct replacement for UTC handling.

https://github.com/openedx/edx-platform/issues/33980

openedx/tests/completion_integration/test_handlers.py

@@ -11,7 +11,7 @@ from completion import handlers
 from completion.models import BlockCompletion
 from completion.test_utils import CompletionSetUpMixin
 from django.test import TestCase
-from pytz import utc
+from zoneinfo import ZoneInfo
 from xblock.completable import XBlockCompletionMode
 from xblock.core import XBlock
 
@@ -66,7 +66,7 @@ class ScorableCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
             usage_id=str(block_key),
             weighted_earned=0.0,
             weighted_possible=3.0,
-            modified=datetime.utcnow().replace(tzinfo=utc),
+            modified=datetime.utcnow().replace(tzinfo=ZoneInfo("UTC")),
             score_db_table='submissions',
             **params
         )
@@ -127,7 +127,7 @@ class ScorableCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
                 usage_id=str(self.block_key),
                 weighted_earned=0.0,
                 weighted_possible=3.0,
-                modified=datetime.utcnow().replace(tzinfo=utc),
+                modified=datetime.utcnow().replace(tzinfo=ZoneInfo("UTC")),
                 score_db_table='submissions',
             )
         mock_handler.assert_called()
@@ -153,7 +153,7 @@ class DisabledCompletionHandlerTestCase(CompletionSetUpMixin, TestCase):
             usage_id=str(self.block_key),
             weighted_earned=0.0,
             weighted_possible=3.0,
-            modified=datetime.utcnow().replace(tzinfo=utc),
+            modified=datetime.utcnow().replace(tzinfo=ZoneInfo("UTC")),
             score_db_table='submissions',
         )
         with pytest.raises(BlockCompletion.DoesNotExist):