fix CRPCCommand args in rpcwallet.cpp

Summary:
While backporting core#19994, I ran into two failing assertions:

• our version of getrawchangeaddress does not have an "address_type" argument
• the "hexstring" for signrawtransactionwithwallet has a typo

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10340