fixed WorkflowStep StepUpdateArguments property types.

[k725]

Summary

#829

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #830 (54444ef) into main (9e783e4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #830   +/-   ##
=======================================
  Coverage   65.89%   65.89%           
=======================================
  Files          13       13           
  Lines        1173     1173           
  Branches      343      343           
=======================================
  Hits          773      773           
  Misses        334      334           
  Partials       66       66           

Impacted Files	Coverage Δ
src/WorkflowStep.ts	91.01% <ø> (ø)

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