[VertexAI] More Swift 6 #988

Job	Run time
pod-lib-lint (ios, macos-14)	3m 44s
pod-lib-lint (macos-15, Xcode_16.2)	3m 47s
spm-package-resolved	1m 44s
sample (macos-13, Xcode_15.2)	1m 32s
spm-unit (macos-13, Xcode_15.2, iOS)	1m 32s
testapp-integration (iOS, macos-15)	1m 47s
spm-unit (macos-14, Xcode_15.4, iOS)	1m 33s
sample (macos-14, Xcode_15.4)	1m 34s
sample (macos-15, Xcode_16.2)	1m 34s
spm-unit (macos-15, Xcode_16.2, iOS)	1m 33s
spm-unit (macos-15, Xcode_16.2, tvOS)	1m 33s
spm-unit (macos-15, Xcode_16.2, macOS)	1m 34s
spm-unit (macos-15, Xcode_16.2, watchOS)	1m 33s
spm-unit (macos-15, Xcode_16.2, catalyst)	1m 32s
spm-unit (macos-15, Xcode_16.2, visionOS)	1m 33s
	28m 5s

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