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

[Erlend E. Aasland]

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


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pull_requests: +25006
pull_request: https://github.com/python/cpython/pull/26412

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<https://bugs.python.org/issue43916>
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