ResourceWarning: unclosed file on buildbots from test_frame

[sweeneyde]

Example warning output from https://buildbot.python.org/all/#/builders/558/builds/802 :

/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py:258: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py' mode='r' encoding='UTF-8'>
ResourceWarning: Enable tracemalloc to get the object allocation traceback
./home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py:258: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py' mode='r' encoding='UTF-8'>
ResourceWarning: Enable tracemalloc to get the object allocation traceback
./home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py:258: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py' mode='r' encoding='UTF-8'>
ResourceWarning: Enable tracemalloc to get the object allocation traceback
./home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py:258: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py' mode='r' encoding='UTF-8'>
ResourceWarning: Enable tracemalloc to get the object allocation traceback
./home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py:258: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py' mode='r' encoding='UTF-8'>
ResourceWarning: Enable tracemalloc to get the object allocation traceback
./home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py:258: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/dje/cpython-buildarea/pull_request.edelsohn-fedora-z.refleak/build/Lib/test/test_frame.py' mode='r' encoding='UTF-8'>
ResourceWarning: Enable tracemalloc to get the object allocation traceback

I believe this is related to the following delicate test case:

cpython/Lib/test/test_frame.py

Lines 238 to 258 in 95d6330

	class TestIncompleteFrameAreInvisible(unittest.TestCase):
	def test_issue95818(self):
	#See GH-95818 for details
	import gc
	self.addCleanup(gc.set_threshold, *gc.get_threshold())
	gc.set_threshold(1,1,1)
	class GCHello:
	def __del__(self):
	print("Destroyed from gc")
	def gen():
	yield
	fd = open(__file__)
	l = [fd, GCHello()]
	l.append(l)
	del fd
	del l
	gen()

Presumably, we could either find a reproducer that doesn't leak resources, or suppress the warnings and/or run the test isolated in a separate process.