fix: Ensure correct ownership for the Rspamd DKIM directory (#3813)

The UID / GID shifted during a new release. Until DKIM handling is refactored in a new major release, this fix ensures the content maintains the expected `_rspamd` ownership.

target/scripts/startup/setup-stack.sh

@@ -94,6 +94,10 @@ function _setup_apply_fixes_after_configuration() {
 
   _log 'debug' 'Removing files and directories from older versions'
   rm -rf /var/mail-state/spool-postfix/{dev,etc,lib,pid,usr,private/auth}
+
+  # /tmp/docker-mailserver/rspamd/dkim
+  _log 'debug' "Ensuring ${RSPAMD_DMS_DKIM_D} is owned by '_rspamd:_rspamd'"
+  chown -R _rspamd:_rspamd "${RSPAMD_DMS_DKIM_D}"
 }
 
 function _run_user_patches() {