Prevent regressions of gitattributes matching vendored /workhorse files

In gitlab!49021 (merged) we fixed an issue caused by .gitattributes rules in gitlab-org/gitlab matching files in gitlab-org/gitlab/workhorse. As long as we are vendoring, it is very impractical to try and have workhorse play by rails's rules.

The reason we missed this in CI is that in gitlab!48690 (merged) I set up basic CI for workhorse using the golang:1.14 docker image. I had trouble with LFS so I hard-disabled it. This hid the problem we would have otherwise noticed.

I am not quite sure how to solve this but "hard disabling LFS" is something we should probably stop doing.