Fix Sphinx warnings in C API doc

Doc/c-api/apiabiversion.rst

@@ -60,7 +60,7 @@ See :ref:`stable` for a discussion of API and ABI stability across versions.
 
    Use this for numeric comparisons, e.g. ``#if PY_VERSION_HEX >= ...``.
 
-   This version is also available via the symbol :data:`Py_Version`.
+   This version is also available via the symbol :c:var:`Py_Version`.
 
 .. c:var:: const unsigned long Py_Version
 

Doc/c-api/arg.rst

@@ -477,7 +477,7 @@ API Functions
    will be set if there was a failure.
 
    This is an example of the use of this function, taken from the sources for the
-   :mod:`_weakref` helper module for weak references::
+   :mod:`!_weakref` helper module for weak references::
 
       static PyObject *
       weakref_ref(PyObject *self, PyObject *args)

Doc/c-api/bool.rst

@@ -13,7 +13,7 @@ are available, however.
 
 .. c:function:: int PyBool_Check(PyObject *o)
 
-   Return true if *o* is of type :c:data:`PyBool_Type`.  This function always
+   Return true if *o* is of type :c:data:`!PyBool_Type`.  This function always
    succeeds.