Issue #26462: Doc: reduce literal_block warnings, fix syntax highlighting.

Patch by Julien Palard.

Doc/tutorial/controlflow.rst

@@ -501,7 +501,9 @@ It could be called like this::
               client="John Cleese",
               sketch="Cheese Shop Sketch")
 
-and of course it would print::
+and of course it would print:
+
+.. code-block:: none
 
    -- Do you have any Limburger ?
    -- I'm sorry, we're all out of Limburger

Doc/tutorial/interpreter.rst

@@ -94,7 +94,9 @@ mode*.  In this mode it prompts for the next command with the *primary prompt*,
 usually three greater-than signs (``>>>``); for continuation lines it prompts
 with the *secondary prompt*, by default three dots (``...``). The interpreter
 prints a welcome message stating its version number and a copyright notice
-before printing the first prompt::
+before printing the first prompt:
+
+.. code-block:: shell-session
 
    $ python3.5
    Python 3.5 (default, Sep 16 2015, 09:25:04)

Doc/tutorial/modules.rst

@@ -140,7 +140,9 @@ the end of your module::
 
 you can make the file usable as a script as well as an importable module,
 because the code that parses the command line only runs if the module is
-executed as the "main" file::
+executed as the "main" file:
+
+.. code-block:: shell-session
 
    $ python fibo.py 50
    1 1 2 3 5 8 13 21 34