Bump actions/download-artifact from 3 to 4 #1979

Job	Run time
build (2_12, mima)	1m 22s
conformance	4m 8s
build (2_12, e2e)	5s
build (2_12, test)	10m 4s
build (2_13, mima)	1m 30s
build (2_13, e2e)	5s
build (2_13, test)	10m 23s
build (3, mima)	6s
build (3, e2e)	8s
build (3, test)	8m 26s
build (2_12, examples_and_formatting)	2m 59s
build (2_13, scala3_compat_test)	6m 49s
build (3, scala3_compat_test)	7m 43s
ci-passed	1s
	53m 49s

Provide feedback