Remove extra comma from reusable can-require-ssh-cert.md

[martindes01]

Why:

• Fixes Double comma in "Enforcing security settings in your Enterprise account" #2571 (double comma in Enforcing security settings in your enterprise account)
• Double comma in reusable can-require-ssh-cert.md (used in enforcing-security-settings-in-your-enterprise-account.md)

What's being changed:

• Remove extra comma from reusable can-require-ssh-cert.md

Check off the following:

• I have reviewed my changes in staging (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the content style guide for GitHub Docs

[megbird]

thank you so much for your contribution! ✨ this will publish as soon as all of our tests pass 🎉

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours.