Fixed registered field having wrong timezone

This happened with at least Postgres, which took it's server's timezone. It's complicated. Let's just set it from our side instead where we have some control.

tests_integration/tests/spool/test_add.py

@@ -1,5 +1,6 @@
 """Integration tests for the Spool API endpoint."""
 
+from datetime import datetime, timezone
 from typing import Any
 
 import httpx
@@ -63,6 +64,10 @@ def test_add_spool_remaining_weight(random_filament: dict[str, Any]):
         "archived": archived,
     }
 
+    # Verify that registered happened almost now (within 1 minute)
+    diff = abs((datetime.now(tz=timezone.utc) - datetime.fromisoformat(spool["registered"])).total_seconds())
+    assert diff < 60
+
     # Clean up
     httpx.delete(f"{URL}/api/v1/spool/{spool['id']}").raise_for_status()