ruff

94947cbf - [ty] Fix merge base calculation for typing-conformance workflow (#19761)

[ty] Fix merge base calculation for typing-conformance workflow (#19761) ## Summary Use `$GITHUB_SHA` (the merged state of `feature` + `main` branch) instead of `{{ github.event.pull_request.head.sha }}` (just the latest `feature` commit) for building the "new" version of `ty` in the typing conformance workflow. ## Test Plan None.