Generate release notes from the published commit

[dwcullop]

Problem

The release workflow invoked git-release-notes without a head ref, so it resolved the head itself instead of being pinned to the commit actually being published. On a release run this can produce release notes for a different commit than the one packaged and tagged.

Change

• Pass --head-ref "$env:GITHUB_SHA" to git-release-notes in .github/workflows/release.yml so the notes are always generated from the exact commit being published.
• Add .github/scripts/Test-ReleaseNotesInvocation.ps1, which validates the git-release-notes command contract (that the workflow invocation supplies the expected arguments) so a future edit that drops --head-ref fails fast.
• Wire that verification step into both .github/workflows/release.yml and .github/workflows/ci-build.yml, extending the existing workflow command-contract validation already performed in CI.

Fixes #1180