[Vertex AI] Fix caching of Vertex AI instances #727

Job	Run time
spm-package-resolved	1m 6s
pod-lib-lint (ios, macos-14)	5m 43s
sample (macos-13, Xcode_15.2)	4m 30s
sample (macos-14, Xcode_15.4)	2m 39s
spm-unit (macos-13, Xcode_15.2, iOS)	6m 0s
sample (macos-15, Xcode_16)	1m 55s
spm-unit (macos-14, Xcode_15.4, iOS)	6m 58s
spm-unit (macos-15, Xcode_16, iOS)	1m 51s
testapp-integration (iOS, macos-15)	3m 1s
spm-unit (macos-15, Xcode_16, tvOS)	1m 43s
spm-unit (macos-15, Xcode_16, macOS)	1m 32s
spm-unit (macos-15, Xcode_16, watchOS)	3m 0s
spm-unit (macos-15, Xcode_16, catalyst)	1m 58s
spm-unit (macos-15, Xcode_16, visionOS)	1m 46s
	43m 42s

Provide feedback