graphics/mesa-devel: unbreak standalone build after 4c2cc95952a6

> Checking for items in pkg-plist which are not in STAGEDIR

Error: Missing: include/vulkan/vulkan_intel.h

PR: 255082
Reported by: Evgeniy Khramtsov
Regressed by: https://gitlab.freedesktop.org/mesa/mesa/-/commit/5e6db1916860

(cherry picked from commit 116c6c13785b89e7cd4f7abe556a9ca960209347)