Fix refcount leak in finalize_remove_modules()

`PyIter_Next()` returns a new reference, but `finalize_remove_modules()`
failed to DECREF `key` when `PyObject_GetItem()`` returns NULL.

Fix by DECREF'ing `key` before continuing.

Signed-off-by: Yongtao Huang <yongtaoh2022@gamil.com>

Author: hyongtao-code

Python/pylifecycle.c

@@ -1622,6 +1622,7 @@ finalize_remove_modules(PyObject *modules, int verbose)
                 PyObject *value = PyObject_GetItem(modules, key);
                 if (value == NULL) {
                     PyErr_FormatUnraisable("Exception ignored while removing modules");
+                    Py_DECREF(key);
                     continue;
                 }
                 CLEAR_MODULE(key, value);