Add unit tests covering Prospect operator field changes

[iamEAP]

What / Why

Although not necessary to exercise every operator in tests (this should be covered by run-crank/typescript-cog-utilities#5), we should at least cover a few new branches of code and ensure the field is set correctly

Scope / UAT Target

• [x] Add operator field assertion in "expected step fields" test for Pardot Prospect Check Step
  • [x] Field is set with expected key
  • [x] Field is set to optional
• [x] Add error outcome assertion when util.compare throws UnknownOperatorError for Pardot Prospect Check Step
• [x] Add error outcome assertion when util.compare throws InvalidOperandError for Pardot Prospect Check Step

[amcpanaligan]

I am not sure for item no. 1. But it seems that there is already an existing check for it. At least for pardot:

[iamEAP]

Oh, sweet! That is all that is intended by item 1.