🐛 SAT: Fix `test_oneof_usage` fail

[keu]

From the slack conv:
https://airbytehq.slack.com/archives/C02URF2BKL1/p1643341400367279

Tell us what happens.
After release of #9768 test_oneof_usage is failing with error:

       for variant_path in variant_paths:
>           top_level_obj = dpath.util.get(self._schema, "/".join(variant_path[:-1]))
E           AttributeError: 'TestSpec' object has no attribute '_schema'

Expected Behavior

test_oneof_usage shouldn't crash the test execution