message: Changelog: Add note for grouping of analysis logs
diff: ## [UNRELEASED]
  - Add this changelog file. [#507](https://github.com/github/codeql-action/pull/507)
  +- Improve grouping of analysis logs. Add a new log group containing a summary of metrics and diagnostics, if they were produced by CodeQL builtin queries. [#515](https://github.com/github/codeql-action/pull/515)
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