Fix memory leak in ElementClass::add_pad_template()

It's taking the pad template as transfer-floating, not transfer-full.

gst-plugin/src/element.rs

@@ -115,7 +115,7 @@ where
         unsafe {
             gst_ffi::gst_element_class_add_pad_template(
                 self as *const Self as *mut gst_ffi::GstElementClass,
-                pad_template.to_glib_full(),
+                pad_template.to_glib_none().0,
             );
         }
     }