Fix 'sleep' invocation incompatiblity between Linux and macOS

TestAuthBeforeLimit is failing on macOS as the sleep call it is using in a custom hook is adding the 's' suffix for seconds. 'sleep' on macOS doesn't support a suffix but expects the input to be seconds. The GNU version also defaults to seconds but accepts a suffix as well. Fix the incompatibility by removing the unnecessary suffix.

Fixes the pipeline failure at: https://gitlab.com/gitlab-org/gitaly/-/pipelines/666638963