Add a missing .gitkeep file
Something went wrong while transferrring gitlab!24000 (merged) to gitlab-foss
, and it is now missing the tmp/tests/.gitkeep
file, which breaks the build.
I'm not sure if this is the right way to add it, but given this is now a difference between the EE and CE codebases, I don't think it's unreasonable.
Closes gitlab#210022 (closed)