Fix a regression in the previous release that broke parsing of some IS0 8601 timestamps. Fixes #2031341 [Calibre corrupts last modified date when using the server](https://bugs.launchpad.net/calibre/+bug/2031341)

timezone() unlike tzoffset() requires timedelta() objects instead of
seconds

src/calibre/utils/iso8601.py

@@ -2,11 +2,10 @@
 # License: GPLv3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 
 
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 
 from calibre_extensions import speedup
 
-
 utc_tz = timezone.utc
 local_tz = datetime.now().astimezone().tzinfo
 UNDEFINED_DATE = datetime(101,1,1, tzinfo=utc_tz)
@@ -23,7 +22,7 @@ def parse_iso8601(date_string, assume_utc=False, as_utc=True, require_aware=Fals
         else:
             sign = '-' if tzseconds < 0 else '+'
             description = "%s%02d:%02d" % (sign, abs(tzseconds) // 3600, (abs(tzseconds) % 3600) // 60)
-            tz = timezone(tzseconds, description)
+            tz = timezone(timedelta(seconds=tzseconds), description)
     elif require_aware:
         raise ValueError(f'{date_string} does not specify a time zone')
     dt = dt.replace(tzinfo=tz)