C API: Report ignored exception in C API functions which ignore all errors

[serhiy-storchaka]

Some C API functions, like PyDict_GetItem() and PyObject_HasAttr() (see capi-workgroup/problems#51 for full list), clears all errors which occurred during execution of these functions. The user has no way to distinguish the normal negative result from error.

There is no way to fix such C API. But at least we can make ignoring errors less unnoticeable. The proposed PR adds _PyErr_WriteUnraisableMsg() when an unrelated error is ignored. It is the same way as reporting errors during object destruction.

Linked PRs

• gh-106672: C API: Report indiscriminately ignored errors #106674