`markdownlint` tests were removed in #10163 due to a security issue in a dependancy ([CVE-2019-10746](https://snyk.io/vuln/SNYK-JS-MIXINDEEP-450212)). According to [snyk](https://snyk.io/test/npm/markdownlint/), `markdownlint` has no currently known vulnerabilities, so we should restore these tests.
markdownlinttests were removed in #10163 due to a security issue in a dependancy (CVE-2019-10746).According to snyk,
markdownlinthas no currently known vulnerabilities, so we should restore these tests.