Update interface-unit-tests.yml pytest warning level handling

[mudit2812]

CI is hiding deprecation warnings, because the use of -W (introduced to support the warnings-as-errors workflow) overrides pytest.ini. This PR moves the creation of the pytest arg to a separate job, and uses the output of this job as the pytest arg. This way, we can avoid using -W altogether if the warnings-as-errors workflow isn't running.

[sc-83043]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

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[rashidnhm]

No worries on the CI changes on the PR. Though I suspect failures to crop up on this PR due to deprecation warnings that may have been suppressed due to this.

I leave fixing that to the PL team, approving within the context of CI changes

[mudit2812]

Going to run the warnings-as-errors workflow to see if it works as expected as well. Run linked here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.54%. Comparing base (afec979) to head (a73823c).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6880   +/-   ##
=======================================
  Coverage   99.54%   99.54%           
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  Files         477      477           
  Lines       45246    45246           
=======================================
  Hits        45042    45042           
  Misses        204      204           

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