CI: Add brute-force workaround for macOS disk image creation failure

Suggestion by GitHub's macOS image maintainer is to kill
XProtectBehaviourService when "Resource busy" error occurs on macOS 13
runners.

.github/scripts/utils.zsh/create_diskimage

@@ -27,6 +27,7 @@ safe_hdiutil() {
 
     if (( _status )) {
       log_warning "Unable to run 'hdiutil ${@}' (attempt #${i}). Retrying."
+      if (( ${+CI} )) sudo pkill -9 XProtect >/dev/null || true
       sleep ${_backoff[${i}]}
     } else {
       break