gh-151515: Redundant cast in asdl_c.py generator

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Bug report

Bug description:

Summary

This PR fixes an undefined behavior bug in the C code generated by Parser/asdl_c.py for get_ast_state().

The Problem

In the generated code, _PyOnceFlag_CallOnce is currently being invoked like this:

_PyOnceFlag_CallOnce(&state->once, (_Py_once_fn_t *)&init_types, state)


### CPython versions tested on:

CPython main branch

### Operating systems tested on:

_No response_

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### Linked PRs
* gh-151514
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