New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/27032#discussion_r538426621

Comment:
```bash
if [ "$XBPS_CHECK_PKGS" ]; then
	configure_args+=" -Dtests=true"
fi
```
is probably a better bet, so we only enable tests when somebody is actually running them.