docs: Fix theck for ignored files
docs: Fix theck for ignored files

The check for ignored header files would break in a distcheck /
out-of-tree build setting.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=46007

freedesktop-unofficial-mirror/ytstenut__ytstenut-glib,freedesktop-unofficial-mirror/ytstenut__ytstenut-glib