bpo-46059: Clarify pattern-matching example in "control flow" docs (GH-30079)

The "Color" example in the pattern-matching section of the "control flow" documentation is not immediately runnable, leading to confusion.

Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>

Doc/tutorial/controlflow.rst

@@ -395,9 +395,11 @@ Several other key features of this statement:
 
       from enum import Enum
       class Color(Enum):
-          RED = 0
-          GREEN = 1
-          BLUE = 2
+          RED = 'red'
+          GREEN = 'green'
+          BLUE = 'blue'
+
+      color = Color(input("Enter your choice of 'red', 'blue' or 'green': "))
 
       match color:
           case Color.RED: