Fix existential-any for Swift6 #335

Job	Run time
swiftpm (iphoneos, arm64)	15s
build (5.10, 15.4, macos-14)	31s
cocoapods	27s
swiftpm (iphonesimulator, x86_64)	17s
build (5.9, 15.2, macos-13)	41s
example (Maps)	1m 8s
swiftpm (iphonesimulator, arm64)	16s
build (5.8, 14.3.1, macos-13)	48s
example (Maps-SwiftUI)	50s
build (5.7, 14.1, macos-12)	16s
example (Stocks)	1m 2s
swiftpm_old (x86_64-apple-ios16.4-simulator, 14.3.1, macos-13)	38s
build (5.6, 13.4.1, macos-12)	16s
example (Samples)	1m 5s
test (17.5, 15.4, iPhone 15 Pro, NO, macos-14)	20m 17s
swiftpm_old (arm64-apple-ios16.4-simulator, 14.3.1, macos-13)	37s
test (16.4, 14.3.1, iPhone 14 Pro, NO, macos-13)	30s
build (5.5, 13.2.1, macos-12)	18s
swiftpm_old (x86_64-apple-ios15.7-simulator, 14.1, macos-12)	35s
test (15.5, 13.4.1, iPhone 13 Pro, NO, macos-12)	19s
swiftpm_old (arm64-apple-ios15.7-simulator, 14.1, macos-12)	37s
	31m 43s

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