docs(block-kit): align workflow button description with docs wording

The docs.slack.dev workflow-button-element page describes this example as
"a section block containing a workflow button element" — match that prose
(was "a section block with a workflow button as an accessory") and keep it
identical to bolt-java-examples.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

Author: zimeg

block-kit/src/elements/workflow_button.py

@@ -13,7 +13,7 @@ def example01() -> SectionBlock:
     Allows users to run a link trigger with customizable inputs.
     https://docs.slack.dev/reference/block-kit/block-elements/workflow-button-element/
 
-    A section block with a workflow button as an accessory.
+    A section block containing a workflow button element.
     """
     block = SectionBlock(
         text=MarkdownTextObject(