Fix #111711: bone collection visibility cannot be overridden

Since the switch from bone layers to bone collections in
998136f7a7, visibility could not be
overridden anymore. Moreso, layer visibility could also be toggled even in linked
state in 3.6 [those changes get lost on file reload, but it was still
useful and expected behavior].

Both are now restored.

Pull Request: https://projects.blender.org/blender/blender/pulls/111775

source/blender/makesrna/intern/rna_armature.cc

@@ -1964,6 +1964,8 @@ static void rna_def_bonecollection(BlenderRNA *brna)
   RNA_def_property_boolean_sdna(prop, nullptr, "flags", BONE_COLLECTION_VISIBLE);
   RNA_def_property_ui_text(
       prop, "Visible", "Bones in this collection will be visible in pose/object mode");
+  RNA_def_property_flag(prop, PROP_LIB_EXCEPTION);
+  RNA_def_property_override_flag(prop, PROPOVERRIDE_OVERRIDABLE_LIBRARY);
   RNA_def_property_update(prop, NC_OBJECT | ND_POSE, nullptr);
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);