Documentation: serial-console: Fix literal block marker

Make rendered text readable by fixing literal block marker, changing
":" to "::".

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230825091626.354352-1-Andrei.Emeltchenko.news@gmail.com

Author: finikorg

Documentation/admin-guide/serial-console.rst

@@ -59,7 +59,7 @@ times. In this case, there are the following two rules:
    the hardware is not available.
 
 The result might be surprising. For example, the following two command
-lines have the same result:
+lines have the same result::
 
 	console=ttyS1,9600 console=tty0 console=tty1
 	console=tty0 console=ttyS1,9600 console=tty1