Update changelog

Author: aeisenberg

extensions/ql-vscode/CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [UNRELEASED]
 
 - Fix bug where a query is sometimes run before the file is saved. [#947](https://github.com/github/vscode-codeql/pull/947)
+- Fix contextual queries that are broken due to a malformed synthetic query suite. [#949](https://github.com/github/vscode-codeql/pull/949)
 
 ## 1.5.4 - 02 September 2021