chore(vertexai): Add corresponding unit test for the fork #5468

Job	Run time
android (tests)	7m 39s
android (packages/cloud_firestore/cloud_firestore/example)	8m 8s
ios (tests)	14m 56s
ios (packages/cloud_firestore/cloud_firestore/example)	25m 50s
macos (tests)	9m 32s
macos (packages/cloud_firestore/cloud_firestore/example)	7m 59s
web (tests)	5m 0s
web (packages/cloud_firestore/cloud_firestore/example)	5m 13s
web-wasm (tests)	4m 27s
web-wasm (packages/cloud_firestore/cloud_firestore/example)	4m 21s
windows	8m 58s
windows-firestore	8m 28s
	1h 50m 31s

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