tests: increase timeout in getnettotals test

Summary:
We saw test failure in a CI run, because the time between the first ping and the last pong was about 4 seconds and the response for getnettotals was not up to date after one second.
Bumping the timeouts from 1 s to 10 s should allow the nodes to synchronize their states and make the test more reliable when it is run on a slow system.

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10723