Fix test copy/paste typo

[ejrgilbert]

No description provided.

[tlively]

Looks right, but curious that the tests weren't previously failing.

[jakobkummerow]

curious that the tests weren't previously failing.

i31.get_s and i31.get_u both trap on (ref.null i31), so this doesn't affect test results.

[jakobkummerow]

LGTM

[tlively]

Ah, I misread and though that this function was used to test non-null cases.