Fix several tests in script_tests.json

Summary:
Several of the tests for the new opcodes did
not indicate properly how many bytes they were
pushing on the stack. They were passing due to
serendipity.

Fixes T324

Test Plan: make check

Reviewers: deadalnix, jasonbcox, matiu, #bitcoin_abc

Reviewed By: jasonbcox, #bitcoin_abc

Subscribers: teamcity

Maniphest Tasks: T324

Differential Revision: https://reviews.bitcoinabc.org/D1291