This object has a finalizer, so once it's no longer referenced, GC can
call that finalizer and then deallocate the storage.
In the case of a failure during construction (e.g., when checking
`validate_obj_is_free_pin_or_none`) this will happen on an incompletely
initialized structure. On samd, in particular, a newly allocated object
(with construct never called) appears to be valid, so GC collecting it
causes deinit() to do things, leading to a hard fault.
The double creation of the UART object was necessary specifically so that
the second allocation would fail. Probably there were other (single
call) ways to make it fail, but this was the easiest / the one discovered
in real life.
Closes: #5493
f94d3e86cf