bpo-41098: Doc: Add missing deprecated directives (GH-21162)

PyUnicodeEncodeError_Create has been deprecated with
`Py_DEPRECATED` macro. But it was not documented.
diff --git a/Include/cpython/pyerrors.h b/Include/cpython/pyerrors.h
index 3f347dc..c2500d9 100644
--- a/Include/cpython/pyerrors.h
+++ b/Include/cpython/pyerrors.h
@@ -145,7 +145,10 @@
     PyObject *filename,
     int lineno);
 
-/* Create a UnicodeEncodeError object */
+/* Create a UnicodeEncodeError object.
+ *
+ * TODO: This API will be removed in Python 3.11.
+ */
 Py_DEPRECATED(3.3) PyAPI_FUNC(PyObject *) PyUnicodeEncodeError_Create(
     const char *encoding,       /* UTF-8 encoded string */
     const Py_UNICODE *object,
@@ -155,7 +158,10 @@
     const char *reason          /* UTF-8 encoded string */
     );
 
-/* Create a UnicodeTranslateError object */
+/* Create a UnicodeTranslateError object.
+ *
+ * TODO: This API will be removed in Python 3.11.
+ */
 Py_DEPRECATED(3.3) PyAPI_FUNC(PyObject *) PyUnicodeTranslateError_Create(
     const Py_UNICODE *object,
     Py_ssize_t length,