Improve highlighting of some code blocks. (GH-6401)

(cherry picked from commit 46936d5a71d1683dbd8ddb6d7f39aab50ecfec50)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Doc/tutorial/appendix.rst b/Doc/tutorial/appendix.rst
index ffd16aa..241a812 100644
--- a/Doc/tutorial/appendix.rst
+++ b/Doc/tutorial/appendix.rst
@@ -52,7 +52,7 @@
 The script can be given an executable mode, or permission, using the
 :program:`chmod` command.
 
-.. code-block:: bash
+.. code-block:: shell-session
 
    $ chmod +x myscript.py