Bump actions/download-artifact from 3 to 4 #375

Job	Run time
Check	31s
Clippy	36s
Rustfmt	11s
MSRV	1m 51s
spellcheck	10s
Test Suite (ubuntu-latest, stable)	5m 41s
Test Suite (ubuntu-latest, nightly)	4m 44s
Test Suite (macos-latest, stable)	10m 25s
Test Suite (macos-latest, nightly)	12m 25s
Test Suite (windows-latest, stable)	7m 52s
Test Suite (windows-latest, nightly)	7m 28s
	51m 54s

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