Fix flaky 'Query.runner(id)' spec

What does this MR do and why?

This MR addresses the failureflaky-test described in #473226 (closed). The problem was that the let_it_be declarations were executed before the time was frozen, meaning that the comparisons were executed against a wrong reference timestamp. I've changed them to let! declarations and reduced the time delta used in the traits to make these cases more obvious.

In addition, I've spotted a minor bug in the Ci::Runner.recent query which was using >= for comparison with the dates, instead of >. The reason the respective spec wasn't failing is because time wasn't frozen there. By adding :freeze_time in the master branch and running the spec, one can see the failure which is then fixed by changing the comparison.

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