[chronik] Bump the RPC timeout in tests

Summary: Most of the chronik tests generate 100 blocks in a row to mature the coinbase utxos. This occasionally times out on qemu CI machine, so let's bump the timeout to avoid the issue.

Test Plan:

./test/functional/test_runner.py chronik_*

Reviewers: #bitcoin_abc, tobias_ruck

Reviewed By: #bitcoin_abc, tobias_ruck

Subscribers: tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D13833