[Scala3] Scala2 src compatibility changes for Scala3 #2851

Job	Run time
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / ci	21m 4s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / compile project with mill	3m 41s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Formatting	1m 37s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Integration Tests	12m 50s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Standard Library (2.13.15)	1m 58s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Benchmarking Sanity Check	2m 42s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Build Mdoc & Website	6m 21s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Test Scala-CLI Example / Build and Test	2m 47s
check tests	1s
all tests passed	1s
Deploy Website	0s
publish	0s
	53m 2s

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