message: Add v2 only prefix to changelog note
diff: ## [UNRELEASED]
  -- The CodeQL Action now runs on Node.js v16. [#1000](https://github.com/github/codeql-action/pull/1000)
  +- [v2+ only] The CodeQL Action now runs on Node.js v16. [#1000](https://github.com/github/codeql-action/pull/1000)
  ## 1.1.5 - 15 Mar 2022
  