gstreamer/miniobject: ToOwned::to_owned() on references has to create a copy

Otherwise it's possible to create a new owned reference from a mutable
reference, and then there is a mutable and immutable reference to the
same data at the same time, which is simply not allowed.

https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/issues/204

gstreamer/src/miniobject.rs

@@ -855,10 +855,7 @@ macro_rules! gst_define_mini_object_wrapper(
             type Owned = $name;
 
             fn to_owned(&self) -> $name {
-                #[allow(clippy::cast_ptr_alignment)]
-                unsafe {
-                    $name($crate::glib::translate::from_glib_none($crate::miniobject::MiniObject::as_ptr(self)))
-                }
+                self.copy()
             }
         }