Update changelog and version after v1.0.5

CHANGELOG.md

@@ -1,5 +1,9 @@
 # CodeQL Action and CodeQL Runner Changelog
 
+## [UNRELEASED]
+
+No user facing changes.
+
 ## 1.0.5 - 12 Jul 2021
 
 - 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)