mailman: Patch out CC modification breaking DKIM/DMARC

The bug[1] would explain all the bounces and unsubscriptions, so patch
it manually until upstream gets it sorted.

[1] https://gitlab.com/mailman/mailman/-/issues/636

roles/mailman/files/mailman.patch

+--- a/usr/lib/python3.10/site-packages/mailman/handlers/avoid_duplicates.py
++++ b/usr/lib/python3.10/site-packages/mailman/handlers/avoid_duplicates.py
+@@ -113,7 +113,3 @@
+                 newrecips.add(r)
+         # Set the new list of recipients.  XXX recips should always be a set.
+         msgdata['recipients'] = list(newrecips)
+-        # RFC 2822 specifies zero or one CC header
+-        del msg['cc']
+-        if cc_addresses:
+-            msg['CC'] = COMMASPACE.join(cc_addresses.values())

roles/mailman/files/patch-mailman.hook

+[Trigger]
+Operation = Install
+Operation = Upgrade
+Type = Package
+Target = mailman3
+
+[Action]
+Description = Patch mailman to not modify the CC header
+When = PostTransaction
+Exec = /usr/bin/bash -c "patch /usr/lib/python*/site-packages/mailman/handlers/avoid_duplicates.py /usr/local/share/mailman.patch"

roles/mailman/tasks/main.yml

@@ -4,6 +4,15 @@
   vars:
     domains: ["{{ lists_domain }}"]
 
+- name: Make pacman hooks directory
+  file: path=/etc/pacman.d/hooks state=directory owner=root group=root mode=0755
+
+- name: Install pacman hook
+  copy: src=patch-mailman.hook dest=/etc/pacman.d/hooks/ owner=root group=root mode=0644
+
+- name: Install mailman patch
+  copy: src=mailman.patch dest=/usr/local/share/ owner=root group=root mode=0644
+
 - name: Install mailman3 and related packages
   pacman: name=mailman3,mailman3-hyperkitty,python-psycopg2,mailman-web,python-xapian-haystack,uwsgi-plugin-python,postfix,postfix-pcre state=present
   register: install