Avoid @mentioning people directly inside Dependabot-created issue descriptions

I got a notification from being mentioned in !313 (merged) because I have the same username on GitHub and contributed to that release of Faker. Dependabot doesn't do this on GitHub by using a redirect URL instead of linking to their actual profile (e.g. in https://github.com/connorshea/vglist/pull/1634).

I'm not sure how you should fix it here, but I'd appreciate it if you did :)

And thanks for building Dependabot support for GitLab, it's a really useful tool! :D