Fix bug in rtdb query get test

[jmwski]

Before this test was trying to shallow-compare the promise object to {foo: 'bar'}.

[changeset-bot]

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Latest commit: dde3a8a

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[google-oss-bot]

Size Analysis Report

Affected Products

No changes between base commit (4986a3e) and head commit (9beded9).

Test Logs

• Base (4986a3e): https://github.com/firebase/firebase-js-sdk/actions/runs/519062618
• Head (9beded9): https://github.com/firebase/firebase-js-sdk/actions/runs/519839339