trio finalizes async gen functions without ResourceWarning on pypy - or if a strong reference is kept

import trio

strong_references = set()

async def amain():
    print(f"{trio.lowlevel.current_task()=}")
    async def agen_fn():
        try:
            yield
        finally:
            print(f"{trio.lowlevel.current_task()=}")

    strong_references.add(agen := agen_fn())

    async for _ in agen:
        break

trio.run(amain)

output with python -W error demo.py:

trio.lowlevel.current_task()=<Task '__main__.amain' at 0x7fc7ff9cf2e0>
trio.lowlevel.current_task()=<Task '<init>' at 0x7fc7ff9cf240>

expected output:

trio.lowlevel.current_task()=<Task '__main__.amain' at 0x7fc7ff9cf2e0>
Exception ignored in: <async_generator object amain.<locals>.agen_fn at 0x7f75a13ef740>
Traceback (most recent call last):
  File "/home/graingert/projects/trio/trio/_core/_asyncgens.py", line 79, in finalizer
    warnings.warn(
ResourceWarning: Async generator '__main__.amain.<locals>.agen_fn' was garbage collected before it had been exhausted. Surround its use in 'async with aclosing(...):' to ensure that it gets cleaned up as soon as you're done using it.
trio.lowlevel.current_task()=<Task '<init>' at 0x7fc7ff9cf240>

Start by running the provided demo with python -W error and compare the behavior on PyPy and when the async generator is strongly referenced. Then inspect trio/_core/_asyncgens.py, especially the finalizer around line 79. Done means the retained or PyPy-finalized unexhausted generator produces the expected ResourceWarning and finalization output.