[3.14] Docs: Fix a grammatical error in Doc/c-api/arg.rst (pythonGH-140525) (pythonGH-140538)

Docs: Fix a grammatical error in `Doc/c-api/arg.rst` (pythonGH-140525)

"have" -> "has"
(cherry picked from commit fc2e23c)

Co-authored-by: RayXu <[email protected]>

Author: miss-islington

Doc/c-api/arg.rst

@@ -160,7 +160,7 @@ There are three ways strings and buffers can be converted to C:
 ``w*`` (read-write :term:`bytes-like object`) [Py_buffer]
    This format accepts any object which implements the read-write buffer
    interface. It fills a :c:type:`Py_buffer` structure provided by the caller.
-   The buffer may contain embedded null bytes. The caller have to call
+   The buffer may contain embedded null bytes. The caller has to call
    :c:func:`PyBuffer_Release` when it is done with the buffer.
 
 ``es`` (:class:`str`) [const char \*encoding, char \*\*buffer]