Fix #958, Convert some UT_GetStubCount to UtAssert_STUB_COUNT

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fixes Convert stub count checks to use UtAssert_STUB_COUNT #958
  • The cases of UT_GetStubCount() which were just being checked via UtAssert_True() have been converted to use UtAssert_STUB_COUNT(), which automatically writes the expected and actual stub count to the test log.

Testing performed
GitHub CI actions all passing successfully.
Local testing with standard cFS suite shows all tests passing and no change in coverage.

Expected behavior changes
No change to code.
Tests also essentially identical, just a bit simpler, clearer and more useful for debugging.

System(s) tested on
Intel(R) Celeron(R) N4100 CPU @ 1.10GHz x86_64
Debian GNU/Linux 11 (bullseye)
Current main branch of cFS.

Contributor Info
Avi Weiss @thnkslprpt

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