fix timezone handling for timestamps from the database

SQLite is not timezone-aware, so make sure to convert to UTC
before inserting any data.

nominatim/tools/convert_sqlite.py

@@ -7,13 +7,14 @@
 """
 Exporting a Nominatim database to SQlite.
 """
-from typing import Set
+from typing import Set, Any
+import datetime as dt
 import logging
 from pathlib import Path
 
 import sqlalchemy as sa
 
-from nominatim.typing import SaSelect
+from nominatim.typing import SaSelect, SaRow
 from nominatim.db.sqlalchemy_types import Geometry, IntArray
 from nominatim.api.search.query_analyzer_factory import make_query_analyzer
 import nominatim.api as napi
@@ -124,12 +125,20 @@ class SqliteWriter:
     async def copy_data(self) -> None:
         """ Copy data for all registered tables.
         """
+        def _getfield(row: SaRow, key: str) -> Any:
+            value = getattr(row, key)
+            if isinstance(value, dt.datetime):
+                if value.tzinfo is not None:
+                    value = value.astimezone(dt.timezone.utc)
+            return value
+
         for table in self.dest.t.meta.sorted_tables:
             LOG.warning("Copying '%s'", table.name)
             async_result = await self.src.connection.stream(self.select_from(table.name))
 
             async for partition in async_result.partitions(10000):
-                data = [{('class_' if k == 'class' else k): getattr(r, k) for k in r._fields}
+                data = [{('class_' if k == 'class' else k): _getfield(r, k)
+                         for k in r._fields}
                         for r in partition]
                 await self.dest.execute(table.insert(), data)