tests: use NO_CHECK_EOF as heredoc limit mark to omit checking code fragments This is a part of preparation to apply checking with check-code.py on code fragments embedded in *.t test scripts. "primes.py" embedded in test-highlight.t causes an error of check-commit.py below: don't use .next(), use next(...) But changing embedded primes.py is painful, because it is committed in test script, and affects hash IDs. On the other hand, primes.py itself is never executed in test script. Therefore, this patch uses NO_CHECK_EOF as heredoc limit mark in order to omit any checking on this code fragments.