New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/39488#discussion_r981147791

Comment:
```suggestion
	mkdir -p webkit2gtk-40 webkit2gtk-50
	(
		cd webkit2gtk-40 && \
		configure_args="${configure_args} -DUSE_SOUP2=ON -DENABLE_WEBDRIVER=OFF" \
		do_configure
	)
	
	(
		cd webkit2gtk-50 && \
		configure_args="${configure_args} -DUSE_GTK4=ON -DENABLE_WEBDRIVER=OFF" \
		do_configure
	)
```
Temporarily manipulating state like working directory or the value of a variable is undesirable and prone to error. Use subshells instead.

Also, because I modified the default args, it seems the default `do_build` run will produce `webkit2gtk41`, so I've swapped `webkit2gtk-41` for `webkit2gtk-40` here. You'll have to double-check my work.