Fix corpus tests

[khieta]

Issue #, if available:

Description of changes:

Hi 👋 I've been working on standardizing Cedar's JSON interfaces (including the integration tests), and made a couple edits recently that will affect cedar-go. I believe the changes I've made here will fix any breaks.

Tested with: go test -count=1 -v -tags corpus ./integration_tests/...

Related PRs:

• Update to cedar: https://github.com/cedar-policy/cedar/pull/837
• Update to cedar-integration-tests: https://github.com/cedar-policy/cedar-integration-tests/pull/4

[philhassey]

I'm holding off merging this until our error alerts for broken tests are working! Thanks!

[patjakdev]

I've added your changes to https://github.com/cedar-policy/cedar-go/pull/22.

The integration tests are now running successfully! Thank you :)