DEV: Use a copy of the fixture file instead of the original one (PR #9645)

There are some rare cases where ./spec/requests/admin/badges_controller_spec.rb:196 fails. The only suspicious thing I found about this spec is that it uses the cropped.png file to test what happens if a non-CSV gets uploaded.

I believe we may be corrupting the original file somehow since we pass it to the UploadCreator. We should use a copy instead.