Update base image to node:20-slim #78

Job	Run time
build / build (linux/arm64, arm64, ubuntu-24.04-arm, true)	1m 2s
build / build (linux/amd64, amd64, ubuntu-latest, true)	44s
build / build (linux/arm/v7, armv7, ubuntu-24.04-arm, false)	52s
merge	21s
	2m 59s

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