[9.20] fix: test: Use UTC timezone when handling keys in kasp test library

When working with key timestamps, ensure we correctly set the UTC
timezone in order for the tests to work consistently regardless of the
local time setting.

Closes #4999

Backport of MR !9673

Merge branch 'backport-4999-pytest-kasp-use-utc-timezone-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!9679

.gitlab-ci.yml

@@ -901,6 +901,7 @@ system:gcc:bookworm:amd64:
   <<: *system_test_gcov_job
   variables:
     CI_ENABLE_ALL_TESTS: 1
+    TZ: Australia/Sydney
   needs:
     - job: unit:gcc:bookworm:amd64
       artifacts: true

bin/tests/system/isctest/kasp.py

@@ -17,8 +17,7 @@ import subprocess
 import time
 from typing import Optional, Union
 
-from datetime import datetime
-from datetime import timedelta
+from datetime import datetime, timedelta, timezone
 
 import dns
 import isctest.log
@@ -54,7 +53,9 @@ class KeyTimingMetadata:
     def __init__(self, timestamp: str):
         if int(timestamp) <= 0:
             raise ValueError(f'invalid timing metadata value: "{timestamp}"')
-        self.value = datetime.strptime(timestamp, self.FORMAT)
+        self.value = datetime.strptime(timestamp, self.FORMAT).replace(
+            tzinfo=timezone.utc
+        )
 
     def __repr__(self):
         return self.value.strftime(self.FORMAT)
@@ -95,7 +96,7 @@ class KeyTimingMetadata:
     @staticmethod
     def now() -> "KeyTimingMetadata":
         result = KeyTimingMetadata.__new__(KeyTimingMetadata)
-        result.value = datetime.now()
+        result.value = datetime.now(timezone.utc)
         return result