Fix 2 rpc_psbt.py Functional Tests

[JaredTate]

This PR fixes 2 rpc_psbt.py functional tests. This one was a pain and had to step through walletcreatefundedpsbt and used this reference to help:
https://developer.bitcoin.org/reference/rpc/walletcreatefundedpsbt.html

FYI: PSBT stands for "Partially Signed Bitcoin Transaction"... we could change name to "PSDT" but that would be a real pain throughout protocol.

To test this:

Compile:

  ./autogen.sh
  ./configure
  make -j 8

Run Specific Functional Tests

test/functional/test_runner.py rpc_psbt.py

[ghost]

Nice work! @JaredTate

[ycagel]

cACK

[gto90]

utACK