ci: Add missing dependency on doxygen sources for docs-generation jobs.

!22191 broke docs generation and marge didn't notice because of missing
 deps.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22271>

docs/doxygen-wrapper.py

@@ -28,6 +28,7 @@ import os
 import subprocess
 import tempfile
 
+# You must update the paths in docs/gitlab-ci.yml's pages job when changing this.
 INPUT_PATHS = [
     'src/compiler/nir/nir.h',
     'src/intel/isl',

docs/gitlab-ci.yml

@@ -24,6 +24,10 @@ pages:
       changes: &docs-or-ci
       - docs/**/*
       - .gitlab-ci.yml
+      # Paths from doxygen-wrapper.py
+      - src/compiler/nir/nir.h
+      - src/intel/isl/**/*
+      - src/vulkan/runtime/**/*
       when: always
     # Other cases default to never