Update Changelog

Author: eysk-io

extensions/ql-vscode/CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Add a command _CodeQL: Run Query on Multiple Databases_, which lets users select multiple databases to run a query on. [#898](https://github.com/github/vscode-codeql/pull/898)
 - Autodetect what language a query targets. This refines the _CodeQL: Run Query on Multiple Databases_ command to only show relevant databases. [#915](https://github.com/github/vscode-codeql/pull/915)
+- Adjust test log output to display diffs only when comparing failed test results with expected test results. [#920](https://github.com/github/vscode-codeql/pull/920)
 
 ## 1.5.2 - 13 July 2021