OverlappingFieldsCanBeMerged throws an error when querying same field w/ and w/o attributes for different union types

[Orrison]

This is a well-known/discussed issue within the GraphQL community and much discussed here: graphql/graphql-js#53

If querying the same field for different union types has the same name but different Type definitions, this should be possible without an alias. But it seems we are currently restricting that within the graphql-php implementation.

[spawnia]

We mostly do what graphql-js does. Can you find a test case for this in https://github.com/graphql/graphql-js/blob/main/src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts or https://github.com/webonyx/graphql-php/blob/master/tests/Validator/OverlappingFieldsCanBeMergedTest.php?