Test Gravatar API Responses

Let's create a new test target that will test the Gravatar API responses to ensure that the Gravatar API responses are what the SDK expects.

Start by locating the existing test targets and the Gravatar API response types in the Swift SDK. Create a test target that exercises the API responses and verifies they match what the SDK expects; completion means the response checks run successfully with the test suite.

Written by the indexing model from the issue text.