ci: pin third-party GitHub Actions to verified release SHAs

[Vamshi-Microsoft]

Purpose

• Pin third-party GitHub Actions to specific release commit SHAs (instead of mutable version tags) for reproducible and immutable workflow runs.
• Replace the tj-actions/changed-files action in the broken-link checker with a built-in git diff step, which removes a third-party dependency from change detection.

Changes:

• .github/workflows/broken-links-checker.yml — replace tj-actions/changed-files with a built-in git diff step; pin lycheeverse/lychee-action to 8646ba3 (v2.8.0).
• .github/workflows/pr-title-checker.yml — pin amannn/action-semantic-pull-request to 48f2562 (v6.1.1).

Does this introduce a breaking change?

• Yes
• No

Golden Path Validation

• I have tested the primary workflows (the "golden path") to ensure they function correctly without errors.

Deployment Validation

• I have validated the deployment process successfully and all services are running as expected with this change.

What to Check

Verify that the following are valid

• ...

Other Information

[Copilot]

Pull request overview

This PR hardens CI workflows by pinning third-party GitHub Actions to immutable release commit SHAs for reproducible runs, and reduces third-party dependency surface by replacing tj-actions/changed-files with a native git diff change-detection step in the broken links workflow.

Changes:

• Pin amannn/action-semantic-pull-request to the v6.1.1 release commit SHA in the PR title checker workflow.
• Replace tj-actions/changed-files with a git diff-based step that emits equivalent outputs (any_changed, all_changed_files) for the broken links workflow.
• Pin lycheeverse/lychee-action to the v2.8.0 release commit SHA in the broken links workflow.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/workflows/broken-links-checker.yml	Removes a third-party changed-files action in favor of git diff and pins lychee-action to an immutable release SHA.
.github/workflows/pr-title-checker.yml	Pins the semantic PR title checker action to an immutable release SHA.

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