Added sleep to avoid test failing because of execution too fast

[SMorettini]

Originating Project/Creator
Affected Component	Svc.PassiveRateGroup

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Change Description

I added a sleep of 1us to simulate some work when the port RateGroupMemberOut is called.

Rationale

The UT of PassiveRateGroup was, sometimes, failing on my laptop because the cycle_time of PassiveRateGroup::CycleIn_handler was smaller than 1 us(it was around 700ns).

The error I was having before the fix :

Fprime/Svc/PassiveRateGroup/test/ut/PassiveRateGroupImplTester.cpp:79: Failure
Expected: (this->tlmHistory_MaxCycleTime->at(0).arg) > (0), actual: 0 vs 0