Merge pull request #118 from da4089/bad-tzname

Fix non-unique TZID when using zoneinfo-derived tzinfo's.

Author: da4089

vobject/icalendar.py

@@ -335,6 +335,10 @@ def pickTzid(tzinfo, allowUTC=False):
         if tzinfo is None or (not allowUTC and tzinfo_eq(tzinfo, utc)):
             return None
 
+        # Try a zoneinfo (CPython 3.9+) first.
+        if hasattr(tzinfo, 'key'):
+            return toUnicode(tzinfo.key)
+
         # Try pytz tzid key
         if hasattr(tzinfo, 'tzid'):
             return toUnicode(tzinfo.tzid)