PackageToJS: Fix skeleton file discovery path for build plugin output #2163

Job	Run time
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	2m 44s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	17m 51s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	13m 43s
format	34s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	13m 42s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	13m 9s
Build for native target (macos-15, Xcode_16.4)	2m 52s
check-bridgejs-generated	2m 42s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 3s
build-examples	26m 27s
deploy-examples	-1s
	1h 36m 46s

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