legacy-query.test.ts: skip if CLI supports new query server

[cklin]

This PR modifies legacy-query.test.ts, which tests integration with the legacy query server in the CodeQL CLI (i.e., codeql execute query-server), to run only for CLI versions that are too old to support the new query server (i.e., codeql execute query-server2). The vscode extension automatically selects the new query server whenever possible, so it should be sufficient to test legacy query server integration only with old CLI versions.

See back-linked internal issue for additional context.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.