Fix body_line_iterator(decode=True) returning no lines in Python 3.11

Python 3.11's body_line_iterator only yields str payloads. When decode=True,
get_payload() returns bytes, which the iterator silently drops — leaving
SimpleMatch, SimpleWarning, and Tagger with nothing to scan.

Remove decode=True (defaulting to False) so get_payload() returns str as
expected. Bounce detection and topic tagging now work correctly under Python 3.

Author: thegushi

Mailman/Bouncers/SimpleMatch.py

@@ -224,7 +224,7 @@ def process(msg, patterns=None):
     # we process the message multiple times anyway.
     for scre, ecre, acre in patterns:
         state = 0
-        for line in email.iterators.body_line_iterator(msg, decode=True):
+        for line in email.iterators.body_line_iterator(msg):
             if state == 0:
                 if scre.search(line):
                     state = 1

Mailman/Bouncers/SimpleWarning.py

@@ -75,7 +75,7 @@ def process(msg):
     addrs = {}
     for scre, ecre, acre in patterns:
         state = 0
-        for line in email.iterators.body_line_iterator(msg, decode=True):
+        for line in email.iterators.body_line_iterator(msg):
             if state == 0:
                 if scre.search(line):
                     state = 1

Mailman/Handlers/Tagger.py

@@ -97,7 +97,7 @@ def scanbody(msg, numlines=None):
     # the first numlines of body text.
     lines = []
     lineno = 0
-    reader = list(email.iterators.body_line_iterator(msg, decode=True))
+    reader = list(email.iterators.body_line_iterator(msg))
     while numlines is None or lineno < numlines:
         try:
             line = reader.pop(0)