test(graphql): add test on anonymous operation warning

[kettanaito]

• Adds a missing test that MSW should warn when capturing an anonymous GraphQL operation that doesn't have a corresponding graphql.operation() handler.
• Improves the request handler's header for anonymous GraphQL operations when printing them in the unhandled request warning/error: anonymous query|mutation (method url) (previously, query|mutation undefined (method url).

What ends up happening now, is that we display the warning even if the user has a permissive graphql.operation() handler in place, which makes no sense.

[codesandbox-ci]

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