bpo-40204, doc: Fix syntax of C variables (GH-21846)

For example, fix the following Sphinx 3 errors:

Doc/c-api/buffer.rst:102: WARNING: Error in declarator or parameters
Invalid C declaration: Expected identifier in nested name. [error at 5]
  void \*obj
  -----^

Doc/c-api/arg.rst:130: WARNING: Unparseable C cross-reference: 'PyObject*'
Invalid C declaration: Expected end of definition. [error at 8]
  PyObject*
  --------^

The modified documentation is compatible with Sphinx 2 and Sphinx 3.

1 files changed, 3 insertions, 3 deletions

diff --git a/Doc/c-api/dict.rst b/Doc/c-api/dict.rst
index 7493837..7694841 100644
--- a/Doc/c-api/dict.rst
+++ b/Doc/c-api/dict.rst
@@ -73,7 +73,7 @@ Dictionary Objects
    .. index:: single: PyUnicode_FromString()
 
    Insert *val* into the dictionary *p* using *key* as a key. *key* should
-   be a :c:type:`const char\*`.  The key object is created using
+   be a :c:type:`const char*`.  The key object is created using
    ``PyUnicode_FromString(key)``.  Return ``0`` on success or ``-1`` on
    failure.  This function *does not* steal a reference to *val*.
 
@@ -116,7 +116,7 @@ Dictionary Objects
 .. c:function:: PyObject* PyDict_GetItemString(PyObject *p, const char *key)
 
    This is the same as :c:func:`PyDict_GetItem`, but *key* is specified as a
-   :c:type:`const char\*`, rather than a :c:type:`PyObject\*`.
+   :c:type:`const char*`, rather than a :c:type:`PyObject*`.
 
    Note that exceptions which occur while calling :meth:`__hash__` and
    :meth:`__eq__` methods and creating a temporary string object
@@ -165,7 +165,7 @@ Dictionary Objects
    prior to the first call to this function to start the iteration; the
    function returns true for each pair in the dictionary, and false once all
    pairs have been reported.  The parameters *pkey* and *pvalue* should either
-   point to :c:type:`PyObject\*` variables that will be filled in with each key
+   point to :c:type:`PyObject*` variables that will be filled in with each key
    and value, respectively, or may be ``NULL``.  Any references returned through
    them are borrowed.  *ppos* should not be altered during iteration. Its
    value represents offsets within the internal dictionary structure, and