Merge branch 'backport-4049-gvariant-docs-dir-glib-2-80' into 'glib-2-80'

Backport !4049 “Correct installation directory of GVariant specification” to glib-2-80

See merge request GNOME/glib!4054
diff --git a/docs/reference/glib/meson.build b/docs/reference/glib/meson.build
index e5e6726..47c5ecf 100644
--- a/docs/reference/glib/meson.build
+++ b/docs/reference/glib/meson.build
@@ -23,7 +23,7 @@
   rst2html5 = find_program('rst2html5', 'rst2html5.py', required: false)
 
   if rst2html5.found()
-    spec_path = docs_dir
+    spec_path = docs_dir / 'glib-2.0'
 
     figures = files(
       'gvariant-byte-boundaries.svg',