Fix 2572, CFE_TIME unit test failure when CFE_MISSION_TIME_AT_TONE_WI…

[dmknutsen]

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Describe the contribution Fix #2572

Sets the clock state to CFE_TIME_SetState_NOT_SET for the external clock source tests such that they complete successfully/provide coverage testing.

Testing performed Successfully executed unit test.

Contributor Info - All information REQUIRED for consideration of pull request Dan Knutsen NASA Goddard