Update gitlab-shell-check location rake task

What does this MR do and why?

As part of Rename bin/check to bin/gitlab-shell-check to t... (gitlab-shell!801 - merged), the binary name was changed. This change updates the binary name in the gitlab:check rake task to match the new name. As of 17.4.0, this check will fail and reports a false-negative failure. The new location is /opt/gitlab/embedded/service/gitlab-shell/bin/gitlab-shell-check. People can use the new location to run the command to check that gitlab-shell is running correctly.

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