Fix `ExperimentalCustomExecutors` SPI import build issues (#552) #2028

Job	Run time
build-examples	43m 58s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 20s
Build for native target (macos-15, Xcode_16.4)	2m 16s
check-bridgejs-generated	2m 45s
format	33s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	13m 46s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	13m 37s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	18m 2s
deploy-examples	8s
	1h 48m 25s

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