Bump the block sync timeout in p2p_ibd_stalling

Summary: The default 60s is not enough to connect 1025 blocks on some of the slowest CI machines.

Test Plan:

./test/functional/test_runner.py p2p_ibd_stalling

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D17663