fix: fix wrong mill source layout #2836

Job	Run time
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / ci	21m 33s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / compile project with mill	3m 27s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Benchmarking Sanity Check	2m 40s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Formatting	1m 28s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Integration Tests	12m 47s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Standard Library (2.13.15)	1m 52s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Build Mdoc & Website	6m 17s
ci (ubuntu-22.04, 8, 2.13.15, 2.4, 7.0) / Test Scala-CLI Example / Build and Test	2m 29s
check tests	1s
all tests passed	1s
publish	0s
Deploy Website	0s
	52m 35s

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