fix client name in dumpwallet output
Summary:
Before:
# Wallet dump created by Bitcoin v0.24.9-382127d03d ...
After:
# Wallet dump created by Bitcoin ABC v0.24.9-382127d03d ...
Test Plan: ninja check-functional
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D10772