message: Update CHANGELOG.md with new limits on uploading SARIF
diff: - These changes will not affect the majority of code scanning workflows. Continue reading only if your workflow uses [@actions/tool-cache](https://github.com/actions/toolkit/tree/main/packages/tool-cache) or relies on the precise location of CodeQL within the Actions tool cache.
  - The tool cache now contains **two** recent CodeQL versions (previously **one**).
  - Each CodeQL version is located under a directory named after the release date and version number, e.g. CodeQL 2.11.6 is now located under `CodeQL/2.11.6-20221211/x64/codeql` (previously `CodeQL/0.0.0-20221211/x64/codeql`).
  +- Bump the maximum number of SARIF runs per file from 15 to 20. This change will help ensure that Code Scanning can process SARIF files generated by third party tools that have many runs. See the [GitHub API documentation](https://docs.github.com/en/rest/code-scanning?apiVersion=2022-11-28#upload-an-analysis-as-sarif-data) for a list of all the limits around uploading SARIF.
  ## 2.1.39 - 18 Jan 2023
  