gh-93738: Documentation C syntax (:c:type:PyInterpreterState * -> :c:expr:PyInterpreterState *) (GH-97777)

:c:type:`PyInterpreterState *` -> :c:expr:`PyInterpreterState *`
(cherry picked from commit 4ebb025)

Co-authored-by: Adam Turner <[email protected]>

Author: AA-Turner

Doc/c-api/init.rst

@@ -867,7 +867,7 @@ code, or when embedding the Python interpreter:
 .. c:type:: PyThreadState
 
    This data structure represents the state of a single thread.  The only public
-   data member is :attr:`interp` (:c:type:`PyInterpreterState *`), which points to
+   data member is :attr:`interp` (:c:expr:`PyInterpreterState *`), which points to
    this thread's interpreter state.