test: Fix flaky wallet_basic test

Summary:

I investigated the issue in core#19876 and I still intend to fix the underlying issue of a race when using wallet RPCs right after starting a node in that PR. However, since that is a bit more complicated than I initially thought it makes sense to merge the fix of the test so the intermittent test failures stop. This fix in the test is going to be needed, either way, #19876 will only provide an error where before it was reporting a false balance

Co-authored-by: João Barbosa <joao.paulo.barbosa@gmail.com>

This is a backport of core#19887

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10183