wallet: ensure change scope is uniform if coin select scope is set
wallet: ensure change scope is uniform if coin select scope is set

In this commit, we fix a regression that was introduced as a result of
the new change scope param. Of cases like spending from an imported
account with PSBT, the change scope should be the same as the coin
selection scope to ensure that a proper change address is available.

Example failure scenario: imported account uses the p2wkh scope, no
other imported accounts, but then we fail when we go to make a change
addr as the imported account hasn't had a p2tr account created.

btcsuite/btcwallet,btcsuite/btcwallet