Merge #14664: example_test.py: fixup coinbase height argument, derive number clearly
Summary:
6c5355e43d example_test.py: fixup coinbase height argument, derive number clearly (Gregory Sanders)
Backport of Core PR14664
Test Plan:
test_runner.py example_test
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D8033