Gate `ExperimentalCustomExecutors` usage behind Swift 6.4 compiler check #2504

Job	Run time
build-examples	20m 0s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	3m 34s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 12s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 8s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	3m 2s
format	35s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	3m 17s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	3m 18s
check-bridgejs-generated	2m 33s
prettier	8s
Build for native target (macos-15, Xcode_16.4)	2m 19s
deploy-examples	0s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	3m 19s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	3m 29s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	3m 14s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	3m 16s
Build for native target (macos-15, Xcode_16.4)	2m 19s
check-bridgejs-generated	2m 33s
prettier	8s
format	35s
build-examples	20m 0s
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 8s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 12s
deploy-examples	-14807s
	-9388s

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