Update `mock-apollo-client` to 0.7.0

What does this MR do?

In this MR, we upgrade a library mock-apollo-client to version 0.7.0. This is necessary to write proper unit tests for GraphQL subscriptions (please see https://github.com/Mike-Gibson/mock-apollo-client/issues/28 for details)

Does this MR meet the acceptance criteria?

Conformity

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  • I have included a changelog entry.
  • I have not included a changelog entry because this is a non-user-facing dependency update.
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