Bump actions/upload-artifact from 3 to 4 #102

Job	Run time
Type-check package	21s
Run linters	33s
Tests on 3.8	1m 1s
Build docs & run doctests	21s
Tests on 3.9	1m 2s
Tests on 3.10	1m 3s
Verify dev env (ubuntu-latest)	25s
Tests on 3.11	59s
Verify dev env (windows-latest)	49s
Tests on 3.12	1m 7s
Verify dev env (macos-latest)	52s
Tests on pypy-3.8	1m 7s
Tests on pypy-3.9	1m 12s
Combine & check coverage.	0s
required-checks-pass	9s
	11m 1s

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