build/meta: Add explicit dependency on Gio-2.0 gir

We depend on Gio for many introspection features (GSettings, GFile...)
without this we'd end up not having many symbols being exposed.

And errors such as
  Warning: Meta: meta_display_add_keybinding: argument settings:
    Unresolved type: 'GSettings*'

As per previous commit we now have this dependency implicitly, but still
it's better to make it clearer in case Clutter would drop it.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3620>

src/meson.build

@@ -1265,6 +1265,7 @@ if have_introspection
     namespace: 'Meta',
     symbol_prefix: 'meta',
     includes: [
+      'Gio-2.0',
       'GObject-2.0',
       'GDesktopEnums-3.0',
       'xlib-2.0',