Bump actions/download-artifact from 4.1.9 to 4.2.1 #1469

Job	Run time
Pre-commit checks / Pre-commit Checks	41s
Check towncrier / Towncrier Checks	21s
Package Rubicon-ObjC / Create Python Package	21s
Unit tests (macos-13, 3.9)	54s
Unit tests (macos-13, 3.12)	45s
Unit tests (macos-13, 3.11)	44s
Unit tests (macos-13, 3.10)	59s
Unit tests (macos-13, 3.13)	44s
Unit tests (macos-14, 3.13)	27s
Unit tests (macos-14, 3.10)	41s
Unit tests (macos-14, 3.12)	27s
Unit tests (macos-14, 3.11)	25s
Unit tests (macos-15, 3.14)	45s
Unit tests (macos-15, 3.12)	27s
Unit tests (macos-15, 3.13)	27s
Unit tests (macos-13, 3.14)	1m 38s
Unit tests (macos-14, 3.14)	43s
Unit tests (macos-15, 3.10)	40s
Unit tests (macos-15, 3.11)	27s
	12m 36s

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