Fix Schema union memberships lookup

[ydah]

Fix a typo in Schema.union_memberships when collecting inherited union memberships without a specific type.

[rmosolgo]

Hey, thanks for sharing this fix. How did you run into this problem?

I'd like to include a test in the project to make sure this code path is properly tested in the future!

[ydah]

Thanks! I found this while reviewing the inheritance paths in Schema.union_memberships, rather than through a production failure. The lookup key didn't match the :union_memberships name used elsewhere.

I've added a regression test that subclasses Dummy::Schema and calls union_memberships without a type. It verifies that the inherited memberships are included.

[rmosolgo]

Got it, that makes sense. Thanks again for this fix!