learn/execution resolver function - should mention signature is specific to js server

From https://github.com/graphql/graphql.github.io/blob/source/src/content/learn/Learn-Execution.md

> A resolver function receives four arguments

I suggest that this is changed to "This resolver function receives four arguments"

Given that the specifications [specifies](https://spec.graphql.org/June2018/#ResolveFieldValue())

> ResolveFieldValue(objectType, objectValue, fieldName, argumentValues)
Let resolver be the internal function provided by objectType for determining the resolved value of a field named fieldName.
Return the result of calling resolver, **providing objectValue and argumentValues.**

So although the resolver function with 4 arguments is specification-compliant a resolver function does not receive four arguments. Only the first two.

Open source/src/content/learn/Learn-Execution.md and find the statement that a resolver function receives four arguments. Review the linked GraphQL specification context, then update the wording to make clear that this four-argument signature is specific to the JavaScript server. Done means the documentation accurately distinguishes this implementation behavior from the specification.

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