[gtk/fix-wayland-subproject-build] Fix build with wayland-protocols subproject

[Matthias Clasen <matthiasc src gnome org>]

commit 06aa640664acbaf7b77560fe216998cc90c58b65
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Feb 10 13:21:28 2022 -0500

    Fix build with wayland-protocols subproject
    
    The missing files() was pointed out in #4530.
    
    Fixes: #4530

 gdk/wayland/meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gdk/wayland/meson.build b/gdk/wayland/meson.build
index 28a00a959b..801d55509a 100644
--- a/gdk/wayland/meson.build
+++ b/gdk/wayland/meson.build
@@ -71,7 +71,7 @@ foreach p: proto_sources
   elif proto_stability == 'staging'
     proto_version = p.get(2)
     output_base = '@0@-@1@'.format(proto_name, proto_version)
-    input = join_paths(wlproto_dir, '@0@/@1@/@2@.xml'.format(proto_stability, proto_name, output_base))
+    input = files(join_paths(wlproto_dir, '@0@/@1@/@2@.xml'.format(proto_stability, proto_name, 
output_base)))
   elif proto_stability == 'private'
     output_base = proto_name
     input = files('protocol/@0@.xml'.format(proto_name))