Bump mypy to 1.9, add to json.encoder, small fixups (#11549)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

stubs/vobject/@tests/stubtest_allowlist.txt

@@ -8,7 +8,6 @@ vobject.win32tz
 
 # dependencies
 vobject.icalendar.Pytz
-vobject.icalendar.pytz
 
 # python2 compat
 vobject.base.basestring
@@ -16,6 +15,7 @@ vobject.base.str_
 vobject.base.to_unicode
 vobject.base.to_basestring
 vobject.vcard.basestring
+vobject.base.unicode_type
 
 # implementation details that users shouldn't depend on
 vobject.base.formatter