Fix Embedded, bump 6.3 Swift toolchain in `test.yml` #2493

Job	Run time
Test BridgeJS against Swift versions (swift:6.1.2, 601.0.0)	3m 11s
check-bridgejs-generated	2m 42s
Test BridgeJS against Swift versions (swift:6.2, 602.0.0)	3m 1s
Build and Test (ubuntu-22.04, https://download.swift.org/development/ubuntu2204/swift-DEVELOPMENT...	8m 30s
Build and Test (ubuntu-24.04, https://download.swift.org/development/ubuntu2404/swift-DEVELOPMENT...	8m 29s
build-examples	7m 53s
format	47s
Build and Test (ubuntu-22.04, https://download.swift.org/swift-6.1-release/ubuntu2204/swift-6.1-R...	8m 29s
prettier	11s
Build for native target (macos-15, Xcode_16.4)	2m 21s
Build and Test (ubuntu-24.04, https://download.swift.org/swift-6.3-branch/ubuntu2404/swift-6.3-DE...	8m 31s
deploy-examples	0s
	54m 5s

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