Fix doxygen errors
Summary:
Identified via -Wdocumentation
Out-of-sequence backport note: the content of psbtwallet.h was moved to wallet.h in D8097, and the doxygen syntax was fixed in the move
This is a backport of Core PR17945
Test Plan: ninja doc-doxygen
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D8620