chore(tests): fix tz warning

Running the tests locally, I get:

```
DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC
```

The recommended upgrade is to use `datetime.now(timezone.utc)` which is
what is done here.

tests/utils.py

@@ -1337,7 +1337,7 @@ def _should_skip(condition=None, until: int = None):
         until = dt.datetime(3000, 1, 1)
     else:
         until = dt.datetime.fromtimestamp(until)
-    if until and dt.datetime.utcnow() < until.replace(tzinfo=None):
+    if until and datetime.now(timezone.utc) < until.replace(tzinfo=None):
         return True
     if condition is not None and not condition:
         return False