chore(ci): pin action version comments to immutable patch tags (#1636)

Tightens `# v6`/`# v3` floating-major comments on SHA-pinned actions to
their exact patch-level tags (`v6.0.2`, `v6.2.0`, `v3.0.1`). Same SHAs,
no behavior change — just removes ambiguity about which release the pin
corresponds to, and keeps the version comment truthful if the upstream
major ever moves.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>