I restarted opendkim several times with systemctl restart opendkim after installing the new opendkim and libopendkim, and it coredumped every time I restarted it:

Feb 25 12:05:12 jik4 systemd-coredump[1357433]: Resource limits disable core dumping for process 1355363 (opendkim).
Feb 25 12:05:12 jik4 systemd-coredump[1357433]: Process 1355363 (opendkim) of user 995 dumped core.
Feb 25 12:05:12 jik4 systemd[1]: opendkim.service: Main process exited, code=dumped, status=6/ABRT
Feb 25 12:05:12 jik4 systemd[1]: opendkim.service: Failed with result 'core-dump'.

I think the process that was exiting coredumped, because when I checked after the coredump there was an opendkim process running.

Then I downgraded and restarted several times; no coredump. Then I upgraded and restarted several times; no coredump. So now I've got the new version of the package and it's not coredumping. :shrug:

Really not sure what to make of this.