Bump actions/download-artifact from 3 to 4 #394

# to view logs

Job	Run time
Build & verify package	29s
Verify dev env (ubuntu-latest)	12s
Verify dev env (windows-latest)	1m 3s
Build docs & run doctests	3s
Type-check API on 3.8	3s
Type-check API on 3.9	4s
Tests on 3.8	3s
Type-check package	2s
Tests on 3.9	4s
Type-check API on 3.10	3s
Tests on 3.10	3s
Type-check API on 3.11	2s
Tests on 3.11	4s
Type-check API on 3.12	2s
Tests on 3.12	2s
Combine & check coverage.	6s
Ensure everything required is passing for branch protection.	2s
	2m 27s

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