fix: annotate get_body's optional return type (CM-1318)

Signed-off-by: Uroš Marolt <uros@marolt.me>

Author: themarolt

services/apps/mailing_list_integration/src/crowdmail/services/parse/noteren.py

@@ -99,7 +99,7 @@ def message_id_cleanup(messageid: str | None) -> str:
 
 # Strongly based on get_payload() from 'b4' (i.e. almost copied directly...)
 # email parsing is rough, charsets are crazy, so let's try to do our best here
-def get_body(msg: email.message.EmailMessage) -> str:
+def get_body(msg: email.message.EmailMessage) -> str | None:
     # walk until we find the first text/plain part
     mcharset = msg.get_content_charset()
     if not mcharset: