[issue43779] Fix possible parser/AST ref leaks

[Erlend Egeberg Aasland]

Change by Erlend Egeberg Aasland <erlend.aasland at innova.no>:


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pull_requests: +24024
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/25289

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43779>
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