adapter.http: Fix reference to constant from the future

Currently, we're using `datetime.UTC`,
a constant defined in the built-in `datetime`
module.

However, this constant was only introduced in
Python version 3.11, as you can see in the
documentation:

- Does not exist in [datetime Python 3.10]
- Exists in [datetime python 3.11]

We did not catch this, as we most likely
programmed the module with Python >= 3.11 and our
CI also ran `mypy` with Python 3.12.

[datetime Python 3.10]: https://docs.python.org/3.10/library/datetime.html#constants
[datetime python 3.11]: https://docs.python.org/3.11/library/datetime.html#datetime.UTC

Fixes eclipse-basyx#330

sdk/basyx/aas/adapter/http.py

@@ -80,7 +80,7 @@ def __init__(self, code: str, text: str, message_type: MessageType = MessageType
         self.code: str = code
         self.text: str = text
         self.message_type: MessageType = message_type
-        self.timestamp: datetime.datetime = timestamp if timestamp is not None else datetime.datetime.now(datetime.UTC)
+        self.timestamp: datetime.datetime = timestamp if timestamp is not None else datetime.datetime.now(datetime.timezone.utc)
 
 
 class Result: