New review comment by Johnnynator on void-packages repository

https://github.com/void-linux/void-packages/pull/31687#discussion_r660023297

Comment:
same as with `do_build` move the last 2 lines to `post_install` and do not overwrite `do_install` at all
```bash
	# python modules
	cd swig/python
	make PYTHON=python3 DESTDIR=${DESTDIR}/ install
```