Bump CLI version from v2.20.7 to v2.21.0 for integration tests (#3991)

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

Author: github-actions[bot]

extensions/ql-vscode/supported_cli_versions.json

@@ -1,4 +1,5 @@
 [
+  "v2.21.0",
   "v2.20.7",
   "v2.19.4",
   "v2.18.4",