Just in case adding is_base_of check for up-casting-ctor of our int…

…erface deleter.

"just in case" b/c `std::unique_ptr` is not allowing invalid casting in the first place,
but I believe such change makes it more explicit (and it was asked for in the first draft review).

include/cetl/pmr/interface_ptr.hpp

@@ -36,7 +36,7 @@ class PmrInterfaceDeleter final
     {
     }
 
-    template <typename Down>
+    template <typename Down, typename = std::enable_if_t<std::is_base_of<Interface, Down>::value>>
     PmrInterfaceDeleter(const PmrInterfaceDeleter<Down>& other)
         : deleter_{other.get_memory_resource(), [other](Interface* ptr) {
                        // Delegate to the down class deleter.