[3.12] GH- gh-111700: Fix syntax highlighting for C code in the "What's New In Python 3.12" documentation (GH-113609) (#113610)

GH- gh-111700: Fix syntax highlighting for C code in the "What's New In Python 3.12" documentation (GH-113609)

Fix PEP 684 syntax highlighting in what's new Python 3.12
(cherry picked from commit 9ce6c01)

Co-authored-by: Parth Doshi <[email protected]>

Author: miss-islington

Doc/whatsnew/3.12.rst

@@ -343,7 +343,9 @@ cores. This is currently only available through the C-API,
 though a Python API is :pep:`anticipated for 3.13 <554>`.
 
 Use the new :c:func:`Py_NewInterpreterFromConfig` function to
-create an interpreter with its own GIL::
+create an interpreter with its own GIL:
+
+.. code-block:: c
 
    PyInterpreterConfig config = {
        .check_multi_interp_extensions = 1,