Doc: C API: Demote sections to subsections for consistency (#126535)

The entire file should be a single section; the headings below the
first heading should be subsections.

Author: rhansen

Doc/c-api/typeobj.rst

@@ -2230,7 +2230,7 @@ This is done by filling a :c:type:`PyType_Spec` structure and calling
 .. _number-structs:
 
 Number Object Structures
-========================
+------------------------
 
 .. sectionauthor:: Amaury Forgeot d'Arc
 
@@ -2344,7 +2344,7 @@ Number Object Structures
 .. _mapping-structs:
 
 Mapping Object Structures
-=========================
+-------------------------
 
 .. sectionauthor:: Amaury Forgeot d'Arc
 
@@ -2381,7 +2381,7 @@ Mapping Object Structures
 .. _sequence-structs:
 
 Sequence Object Structures
-==========================
+--------------------------
 
 .. sectionauthor:: Amaury Forgeot d'Arc
 
@@ -2461,7 +2461,7 @@ Sequence Object Structures
 .. _buffer-structs:
 
 Buffer Object Structures
-========================
+------------------------
 
 .. sectionauthor:: Greg J. Stein <[email protected]>
 .. sectionauthor:: Benjamin Peterson
@@ -2556,7 +2556,7 @@ Buffer Object Structures
 
 
 Async Object Structures
-=======================
+-----------------------
 
 .. sectionauthor:: Yury Selivanov <[email protected]>
 
@@ -2624,7 +2624,7 @@ Async Object Structures
 .. _slot-typedefs:
 
 Slot Type typedefs
-==================
+------------------
 
 .. c:type:: PyObject *(*allocfunc)(PyTypeObject *cls, Py_ssize_t nitems)
 
@@ -2733,7 +2733,7 @@ Slot Type typedefs
 .. _typedef-examples:
 
 Examples
-========
+--------
 
 The following are simple examples of Python type definitions.  They
 include common usage you may encounter.  Some demonstrate tricky corner