Issue #22932: Fix timezones in email.utils.formatdate.

Patch from Dmitry Shachnev.

Lib/email/utils.py

@@ -155,30 +155,14 @@ def formatdate(timeval=None, localtime=False, usegmt=False):
     # 2822 requires that day and month names be the English abbreviations.
     if timeval is None:
         timeval = time.time()
-    if localtime:
-        now = time.localtime(timeval)
-        # Calculate timezone offset, based on whether the local zone has
-        # daylight savings time, and whether DST is in effect.
-        if time.daylight and now[-1]:
-            offset = time.altzone
-        else:
-            offset = time.timezone
-        hours, minutes = divmod(abs(offset), 3600)
-        # Remember offset is in seconds west of UTC, but the timezone is in
-        # minutes east of UTC, so the signs differ.
-        if offset > 0:
-            sign = '-'
-        else:
-            sign = '+'
-        zone = '%s%02d%02d' % (sign, hours, minutes // 60)
+    if localtime or usegmt:
+        dt = datetime.datetime.fromtimestamp(timeval, datetime.timezone.utc)
     else:
-        now = time.gmtime(timeval)
-        # Timezone offset is always -0000
-        if usegmt:
-            zone = 'GMT'
-        else:
-            zone = '-0000'
-    return _format_timetuple_and_zone(now, zone)
+        dt = datetime.datetime.utcfromtimestamp(timeval)
+    if localtime:
+        dt = dt.astimezone()
+        usegmt = False
+    return format_datetime(dt, usegmt)
 
 def format_datetime(dt, usegmt=False):
     """Turn a datetime into a date string as specified in RFC 2822.