[Cashtab] Add missing input param to unit test

Summary: Missing a function param in a unit test. Test is passing bc it is confirming an error is thrown, and the desired error is thrown before the feeRate param is used in the function.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D15182