test: add TodoCognitoMultiOwner to watchOS target for DataStore test

[lawmicha]

Issue #

Related PR with test issue #3223

Description

Test is missing file added to watchOS target (https://github.com/aws-amplify/amplify-swift/actions/runs/6340116424/job/17222695667#logs)

❌  /Users/runner/work/amplify-swift/amplify-swift/AmplifyPlugins/DataStore/Tests/DataStoreHostApp/AWSDataStorePluginAuthCognitoTests/AWSDataStoreCategoryPluginAuthOwnerIntegrationTests.swift:225:47: cannot find 'TodoCognitoMultiOwner' in scope

            ModelRegistry.register(modelType: TodoCognitoMultiOwner.self)
                   ^~~~~~~~~~~~~~~~~~~~~

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.