Update CHANGELOG

Author: aeisenberg

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [UNRELEASED]
 
 - The `analyze` step of the Action now supports a `skip-queries` option to merely build the CodeQL database without analyzing. This functionality is not present in the runner. Additionally, the step will no longer fail if it encounters a finalized database, and will instead continue with query execution. [#602](https://github.com/github/codeql-action/pull/602)
+- Update the warning message when the baseline lines of code count is unavailable. [#608](https://github.com/github/codeql-action/pull/608)
 
 ## 1.0.4 - 28 Jun 2021