Scope push to the default branch in copilot-setup-steps samples

The sample `copilot-setup-steps.yml` workflow triggered on both `push` and
`pull_request` with the same `paths` filter. For a branch pushed to the same
repository, both events fire on the same commit, so the workflow ran twice and
produced two identical check runs on the pull request.

Limit the `push` trigger to the default branch. Changes on any other branch are
still validated through the `pull_request` trigger (including pull requests from
forks, which `push` does not cover in the base repository), and the workflow
still runs when the file lands on the default branch.

Fixes #42379

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FuL8Cm3afpXSBiiGnUo7FA

Author: claude

content/copilot/how-tos/copilot-on-github/customize-copilot/customize-cloud-agent/customize-the-agent-environment.md

@@ -58,7 +58,11 @@ name: "Copilot Setup Steps"
 # allow manual testing through the repository's "Actions" tab
 on:
   workflow_dispatch:
+  # Limit `push` to your default branch. Changes on any other branch are already validated
+  # by the `pull_request` trigger, so this avoids two runs for the same commit.
   push:
+    branches:
+      - main
     paths:
       - .github/workflows/copilot-setup-steps.yml
   pull_request:

content/copilot/tutorials/cloud-agent/improve-a-project.md

@@ -98,6 +98,8 @@ Creating this file is optional but is a good idea if you use {% data variables.c
    on:
      workflow_dispatch:
      push:
+       branches:
+         - main
        paths:
          - .github/workflows/copilot-setup-steps.yml
      pull_request: