Inherit from BaseResolver in specs

What does this MR do and why?

Inherit from BaseResolver in specs

When creating resolver classes for use in specs, we should still inherit from BaseResolver since initializing a field now calls some methods on the resolver

When upgrading to GraphQL 2.x, this results in spec failures like: https://gitlab.com/gitlab-org/gitlab/-/jobs/5131348861.

This is extracted from !88733 (merged) to make it easier to review

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Related to #363131 (closed)