New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/27028#discussion_r538478240

Comment:
Please change `pre_build` to `post_patch`. `pre_build` only runs during the build stage, but sometimes it is nice to verify that the patching had the intended effect by running `xbps-src patch` without triggering the build stage.