Fix error message in dependency resolution jobs

What does this MR do and why?

When adding the two inputs for the timeouts, in the error messages was overlooked that backticks open subshells and can't be used for a markdown-like message. Changing them to single quotes removes the error:

resolution_jobs_checkout_timeout: command not found
resolution_jobs_script_timeout: command not found
[…] Use  and  to configure this value.

References

gitlab-org/gitlab!249426 (comment 3725059620)

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