Update workflow triggers for Copilot setup

Remove pull_request trigger for copilot-setup-steps workflow.

Author: brignano

content/copilot/how-tos/use-copilot-agents/coding-agent/customize-the-agent-environment.md

@@ -55,9 +55,6 @@ on:
   push:
     paths:
       - .github/workflows/copilot-setup-steps.yml
-  pull_request:
-    paths:
-      - .github/workflows/copilot-setup-steps.yml
 
 jobs:
   # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.