tools: update unified-args to 7.0.0 for md-lint CLI

Update unified-args from 6.0.0 to 7.0.0 for
tools/node-lint-md-cli-rollup. This removes a vulnerable package
([email protected]) from the dependencies.

Refs: https://app.snyk.io/vuln/SNYK-JS-SETVALUE-450213

PR-URL: #28434
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Jiawen Geng <[email protected]>