Manually update the CHANGELOG

This should have happened in a mergeback PR, but the workflow to
generate this was broken.

Author: aeisenberg

CHANGELOG.md

@@ -1,7 +1,9 @@
 # CodeQL Action and CodeQL Runner Changelog
 
+## [UNRELEASED]
+
 ## 1.0.0 - 31 May 2021
 
 - 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)
-- Add metrics and diagnostics summaries from custom query suites to the analysis summary log group. [#532](https://github.com/github/codeql-action/pull/532) 
+- Add metrics and diagnostics summaries from custom query suites to the analysis summary log group. [#532](https://github.com/github/codeql-action/pull/532)