gtk-doc: move back to EAPI=6

The downgrade to EAPI=5 missed the eapply statement.
Now that we support EAPI=6, move back up.

BUG=chromium:1026092
TEST=`sudo emerge gtk-doc` works

Change-Id: I97418397f750e7b94c08bf004ccc6f9cfbf46e57
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/portage-stable/+/1923013
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed