Fix Playwright workflow to fetch base branch for PR comparison

[Copilot]

Problem

The Playwright workflow in .github/workflows/playwright.yml fails to detect modified projects in pull request contexts, causing the samples/find-changes.sh script to return empty results and skip running tests on changed samples.

Root Cause: The workflow attempts to compare changes against origin/${{ github.base_ref }} (e.g., origin/main), but GitHub Actions checkout@v4 only fetches the current branch (PR branch) by default. When find-changes.sh tries to run:

git diff --name-only --diff-filter=AM origin/main HEAD -- "samples/"

It fails with:

fatal: bad revision 'origin/main'

Solution

Add a step after actions/checkout@v4 to explicitly fetch the base branch for PR events:

- name: Fetch base branch for PR comparison
  if: github.event_name == 'pull_request'
  run: git fetch origin ${{ github.base_ref }}:${{ github.base_ref }}

This step:

• Only runs for pull_request events (not push events)
• Fetches the base branch from origin and creates a local tracking reference
• Ensures the origin/main reference exists locally for comparison

Testing

• ✅ Verified the fix resolves the "bad revision 'origin/main'" error
• ✅ Confirmed change detection works correctly with the fetched base branch
• ✅ Validated the step only runs for pull_request events
• ✅ Ensured YAML syntax is valid and no existing functionality is broken
• ✅ Tested end-to-end change detection with actual file modifications

Impact

This fix ensures that PR workflows properly detect modified projects, allowing Playwright tests to run on the correct samples rather than being skipped due to empty change detection results.

This pull request was created as a result of the following prompt from Copilot chat.

The Playwright workflow in .github/workflows/playwright.yml fails to detect modified projects in pull request contexts, because it attempts to compare changes against a base branch ref (origin/${{ github.base_ref }}) which may not be present locally after checkout. This causes the samples/find-changes.sh script to return empty results. To fix this, add a step after the checkout to explicitly fetch the base branch for PR events, ensuring the ref exists locally for comparison. Insert the following step after 'actions/checkout@v4' in jobs.pr_and_push_tests.steps:

• name: Fetch base branch for PR comparison
  if: github.event_name == 'pull_request'
  run: git fetch origin ${{ github.base_ref }}:${{ github.base_ref }}

This ensures the base branch is available for the find-changes.sh script, so modified projects are detected correctly in PRs.

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