ffi: restore _PyImport_FindExtensionObject on Python 3.10

This symbol was initially removed from 3.10. But it was restored
late in the 3.10 development cycle in time for 3.10.0. See
https://bugs.python.org/issue45307.

CHANGELOG.md

@@ -45,6 +45,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Move Py_DecodeLocale from sysmodule to fileutils. [#1887](https://github.com/PyO3/pyo3/pull/1887)
 - Deprecate `PySys_AddWarnOption`, `PySys_AddWarnOptionUnicode` and `PySys_HasWarnOptions`. [#1887](https://github.com/PyO3/pyo3/pull/1887)
 - Remove function PyTuple_ClearFreeList from python 3.9 above. [#1887](https://github.com/PyO3/pyo3/pull/1887)
+- The `_PyImport_FindExtensionObject` FFI binding is now available to Python 3.10. The symbol is not present in some 3.10 release candidates but is present in the final release. [#1942](https://github.com/PyO3/pyo3/pull/1942)
 
 ### Fixed
 

src/ffi/cpython/import.rs

@@ -16,7 +16,6 @@ extern "C" {
     pub fn _PyImport_FindBuiltin(name: *const c_char) -> *mut PyObject;
     #[cfg(all(Py_3_7, not(Py_3_9)))]
     pub fn _PyImport_FindBuiltin(name: *const c_char, modules: *mut PyObject) -> *mut PyObject;
-    #[cfg(not(Py_3_10))]
     pub fn _PyImport_FindExtensionObject(a: *mut PyObject, b: *mut PyObject) -> *mut PyObject;
     #[cfg(not(Py_3_7))]
     pub fn _PyImport_FixupBuiltin(module: *mut PyObject, name: *const c_char) -> c_int;