Prompted by recent changes in fontconfig and its handling of
/usr/local/share/fonts, I noticed that asterisk also creates a directory
below /usr/local with mode 2775 and owner root:staff.

According to Policy §9.1.2, since Policy 4.1.4 (2018), directories below
/usr/local should normally be created with mode 0755 and owner
root:root, a change that was made to avoid privilege escalation by
members of the staff group. (There's a flag file to opt back in to the
old behaviour.)

Instead of open-coding the necessary logic, I would suggest using
dh_usrlocal to create this directory. The procedure to do that is
something like this:

1. create debian/asterisk/usr/local/share/asterisk/sounds
   (for example with `install -d` in d/rules, or probably using
   debian/asterisk.dirs would also work)
2. make sure dh_usrlocal is run (normally dh will run it)
3. remove open-coded logic in maintainer scripts to create (and possibly
   remove) this directory
4. make sure the #DEBHELPER# placeholder appears in any maintainer scripts
   that still exist

dh_usrlocal will insert maintainer script snippets generated from
/usr/share/debhelper/autoscripts/ to create and remove the directories
when appropriate.

Thanks,
    smcv