Bump CLI version from v2.20.5 to v2.20.6 for integration tests (#3955)

Co-authored-by: github-actions[bot] <[email protected]>

Author: github-actions[bot]

extensions/ql-vscode/supported_cli_versions.json

@@ -1,5 +1,5 @@
 [
-  "v2.20.5",
+  "v2.20.6",
   "v2.19.4",
   "v2.18.4",
   "nightly"