Update interface-unit-tests.yml handling of pytest warnings

[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]

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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 99.59%. Comparing base (0ed7395) to head (1ba716a).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6880   +/-   ##
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  Coverage   99.59%   99.59%           
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  Files         479      479           
  Lines       45399    45399           
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  Hits        45215    45215           
  Misses        184      184           

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[JerryChen97]

After we make sure no unexpected warnings from return_type, I guess it will be better to add labels of full CI and GPU to this PR