update confgs in tests to use helper functions

[gulsumgudukbay]

Description

There were new UTs added to upstream, and they do not have decoupled config helper function usage. This PR adds that

Tests

Ran all the tests using:
.venv_rocm_jax082_decoupled/bin/python3 -m pytest -m decoupled -v tests --csv=decoupled-tests-report.csv --html=decoupled-tests-report.html --self-contained-html 2>&1 | tee maxtext_decoupled_UT.log

No tests fail with config errors.

Checklist

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