gh-144759: Fix NEWS entry to use plain markup for internal functions

Replace :c:func: references with double-backtick markup since these
are internal functions without documentation entries.

Author: raminfp

Misc/NEWS.d/next/Core_and_Builtins/2026-02-13-12-00-00.gh-issue-144759.d3qYpe.rst

@@ -1,4 +1,4 @@
 Fix undefined behavior in the lexer when ``start`` and ``multi_line_start``
-pointers are ``NULL`` in :c:func:`_PyLexer_remember_fstring_buffers` and
-:c:func:`_PyLexer_restore_fstring_buffers`. The ``NULL`` pointer arithmetic
+pointers are ``NULL`` in ``_PyLexer_remember_fstring_buffers()`` and
+``_PyLexer_restore_fstring_buffers()``. The ``NULL`` pointer arithmetic
 (``NULL - valid_pointer``) is now guarded with explicit ``NULL`` checks.