gh-111178: Fix function signatures for test_capi

[vstinner]

• Issue: UBSan: Calling a function through pointer to incorrect function type is undefined behavior #111178

[picnixz]

Just to be consistent with the rest of your added code and the existing code (for *const *args). Btw, just check if you need to remove redundant casts for the affected functions.

[vstinner]

Just to be consistent with the rest of your added code and the existing code (for *const *args).

I applied your suggestions.

Btw, just check if you need to remove redundant casts for the affected functions.

Done: I checked all modified functions. There was no cast before.