[issue43916] Mark static types newly converted to heap types as immutable: add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag

[STINNER Victor]

Change by STINNER Victor <vstinner at python.org>:


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pull_requests: +24441
pull_request: https://github.com/python/cpython/pull/25751

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue43916>
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