The webassembly port needs some additional weakref tests due to the fact
that garbage collection only happens when Python execution finishes and
JavaScript resumes.
The `tests/ports/webassembly/heap_expand.py` expected output also needs to
be updated because the amount of GC heap got smaller (weakref WTB takes
some of the available RAM).
Signed-off-by: Damien George <damien@micropython.org>
Damien George