allow multiple error blocks from a single path

[savaki]

Currently, only a single error block will be generated from a given path. With the advent of the Unwrap() []error interface that builtin methods like errors.Join provide, graphql should treat this as multiple errors for the same path

[pavelnikolov]

This is against the GraphQL spec, which clearly states:

If the field returns null because of a field error which has already been added to the "errors" list in the response, the "errors" list must not be further affected. That is, only one error should be added to the errors list per field.

https://spec.graphql.org/October2021/#sel-EANRNDLAACNAn7V