bpo-36346: Document removal schedule of deprecate APIs (GH-20879)

We will remove wstr cache in Python 3.12. See PEP 623.
diff --git a/Doc/c-api/arg.rst b/Doc/c-api/arg.rst
index a91b3c7..1d93b35 100644
--- a/Doc/c-api/arg.rst
+++ b/Doc/c-api/arg.rst
@@ -149,7 +149,7 @@
       Previously, :exc:`TypeError` was raised when embedded null code points
       were encountered in the Python string.
 
-   .. deprecated-removed:: 3.3 4.0
+   .. deprecated-removed:: 3.3 3.12
       Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
       :c:func:`PyUnicode_AsWideCharString`.
 
@@ -158,7 +158,7 @@
    Unicode data buffer, the second one its length.  This variant allows
    null code points.
 
-   .. deprecated-removed:: 3.3 4.0
+   .. deprecated-removed:: 3.3 3.12
       Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
       :c:func:`PyUnicode_AsWideCharString`.
 
@@ -166,7 +166,7 @@
    Like ``u``, but the Python object may also be ``None``, in which case the
    :c:type:`Py_UNICODE` pointer is set to ``NULL``.
 
-   .. deprecated-removed:: 3.3 4.0
+   .. deprecated-removed:: 3.3 3.12
       Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
       :c:func:`PyUnicode_AsWideCharString`.
 
@@ -174,7 +174,7 @@
    Like ``u#``, but the Python object may also be ``None``, in which case the
    :c:type:`Py_UNICODE` pointer is set to ``NULL``.
 
-   .. deprecated-removed:: 3.3 4.0
+   .. deprecated-removed:: 3.3 3.12
       Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
       :c:func:`PyUnicode_AsWideCharString`.