PEP 646: Fix typo in the example code (#1808)

pep-0636.rst

@@ -401,7 +401,7 @@ each element looking for example like these:
 Until now, our patterns have processed sequences, but there are patterns to match
 mappings based on their present keys. In this case you could use::
 
-    for action in message:
+    for action in actions:
         match action:
             case {"text": message, "color": c}:
                 ui.set_text_color(c)
@@ -437,7 +437,7 @@ are both strings. For many builtin classes (see PEP-634 for the whole list), you
 use a positional parameter as a shorthand, writing ``str(c)`` rather than ``str() as c``.
 The fully rewritten version looks like this::
 
-    for action in message:
+    for action in actions:
         match action:
             case {"text": str(message), "color": str(c)}:
                 ui.set_text_color(c)