Add md line break to stale-issues.yml

I just read https://gitlab.com/gitlab-org/gitlab-ce/issues/60192 and thought I found a typo. Turned out it was not, but an appearance of https://gitlab.com/gitlab-org/gitlab-ce/issues/57809. Since md does not apply single line breaks that formatting did not get applied and thus the wrong looking result. I changed that now adding punctuation and two spaces at the end of the line which applies a single line break in md. I hope this is the correct way.

There might be other occurrences of this problem, so it might be worth to check other places (in this and other files) as well.