Fix #1498, update ut_oscore_test.c to run OS_TaskFindIdBySystemData only once

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Fix #1498, update ut_oscore_test.c to run OS_TaskFindIdBySystemData only once

[BEGIN] 43 OS_TaskFindIdBySystemData
[ PASS] 43.001 ut_oscore_task_test.c:621 - OS_TaskFindIdBySystemData(NULL, &sysdata, sizeof(sysdata)) (-2) == OS_INVALID_POINTER (-2)
[ PASS] 43.002 ut_oscore_task_test.c:622 - OS_TaskFindIdBySystemData(&task_id, NULL, sizeof(sysdata)) (-2) == OS_INVALID_POINTER (-2)
[ PASS] 43.003 ut_oscore_task_test.c:623 - OS_TaskFindIdBySystemData(&task_id, &sysdata, 0) (-2) == OS_INVALID_POINTER (-2)
[ INFO]                        ABORT::0     WARN::0     FLOW::0     DEBUG::0     N/A::0   
[  END] 43 OS_TaskFindIdBySystemData TOTAL::3     PASS::3     FAIL::0     MIR::0     TSF::0     TTF::0   

Testing performed
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1. make ENABLE_UNIT_TESTS=true install
2. run osal_core_UT

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• API Change: xxx (if applicable)
• Behavior Change: xxx (if applicable)
• Or no impact to behavior

System(s) tested on

• Hardware: [e.g. PC, SP0, MCP750]
• OS: [e.g. Ubuntu 18.04, RTEMS 4.11, VxWorks 6.9]
• Versions: [e.g. cFE 6.6, OSAL 4.2, PSP 1.3 for mcp750, any related apps or tools]

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Anh Van, GSFC