Hide VSCode console output

Most of the warnings that are currently being shown in CI are coming
from VSCode. We can hide the VSCode output to make the CI logs more
readable. This should not influence the tests; the output of tests
(in particular using `console.log`/`console.error` etc.) will still be
shown.

See: 0c98dc12ad/packages/jest-runner-vscode/src/public-types.ts (L58-L68)

extensions/ql-vscode/test/vscode-tests/jest-runner-vscode.config.base.js

@@ -13,6 +13,8 @@ const config = {
     "--extensions-dir=" + path.join(rootDir, ".vscode-test", "extensions"),
   ],
   extensionDevelopmentPath: rootDir,
+  // Hide VSCode stdout, but show console.log
+  filterOutput: true,
 };
 
 if (process.env.VSCODE_INSPECTOR_OPTIONS) {