Docs: Correct formatting of a multiline code block (GH-13806)

(cherry picked from commit bd26a4466b507e196fc9a5e4a6cb7cd6d39f85aa)

Co-authored-by: Joseph Fox-Rabinovitz <madphysicist@users.noreply.github.com>
diff --git a/Doc/c-api/buffer.rst b/Doc/c-api/buffer.rst
index 72d9650..7553efc 100644
--- a/Doc/c-api/buffer.rst
+++ b/Doc/c-api/buffer.rst
@@ -355,8 +355,10 @@
 a standard n-dimensional C-array. Otherwise, the consumer must access an
 n-dimensional array as follows:
 
-   ``ptr = (char *)buf + indices[0] * strides[0] + ... + indices[n-1] * strides[n-1]``
-   ``item = *((typeof(item) *)ptr);``
+.. code-block:: c
+
+   ptr = (char *)buf + indices[0] * strides[0] + ... + indices[n-1] * strides[n-1];
+   item = *((typeof(item) *)ptr);
 
 
 As noted above, :c:member:`~Py_buffer.buf` can point to any location within