scripted-diff: Use getInt<T> over get_int/get_int64
Summary:
Replace-only diff with no change in behavior.
Backport of core#25153.
Depends on D16272.
Test Plan:
ninja all check-all
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Differential Revision: https://reviews.bitcoinabc.org/D16273