Fix typo in std::mem::transmute causing UB while using AsArg<DynGd<Base, D>>.

Author: Yarwin

godot-core/src/meta/args/as_arg.rs

@@ -178,7 +178,7 @@ where
     {
         if T::IS_SAME_CLASS {
             // SAFETY: T == Base, so &DynGd<T, D> can be treated as &DynGd<Base, D>.
-            let gd_ref = unsafe { std::mem::transmute::<&Gd<T>, &DynGd<Base, D>>(self) };
+            let gd_ref = unsafe { std::mem::transmute::<&DynGd<T, D>, &DynGd<Base, D>>(self) };
             CowArg::Borrowed(gd_ref)
         } else {
             // Different types: clone and upcast. May incur ref-count increment for RefCounted objects, but the common path

itest/rust/src/object_tests/dyn_gd_test.rs

@@ -431,11 +431,18 @@ fn dyn_gd_store_in_godot_array() {
 }
 
 #[itest]
-fn dyn_gd_as_arg() {
+fn dyn_gd_as_arg_inherited_base() {
     let refc_health = Gd::from_object(RefcHealth { hp: 42 }).into_dyn();
     let node_health = foreign::NodeHealth::new_alloc().into_dyn();
     let typed_none = None::<&DynGd<RefcHealth, dyn Health>>;
 
+    // Array<DynGd<Base, D>>.
+    // See: https://github.com/godot-rust/gdext/pull/1345.
+    let array: Array<DynGd<RefcHealth, dyn Health>> = array![&refc_health];
+    assert_eq!(array.len(), 1);
+    let first = array.at(0);
+    assert_eq!(first.dyn_bind().get_hitpoints(), 42);
+
     // Array<DynGd>.
     let array: Array<DynGd<Object, dyn Health>> = array![&refc_health, &node_health];
     assert_eq!(array.len(), 2);