Bump tox from 4.20.0 to 4.21.2 #1245

Job	Run time
Check towncrier / Towncrier Checks	23s
Package Rubicon-ObjC / Create Python Package	12s
Pre-commit checks / Pre-commit Checks	24s
Unit tests (macos-12, 3.8)	43s
Unit tests (macos-12, 3.9)	42s
Unit tests (macos-12, 3.10)	56s
Unit tests (macos-12, 3.11)	40s
Unit tests (macos-12, 3.12)	44s
Unit tests (macos-12, 3.13-dev)	1m 13s
Unit tests (macos-13, 3.8)	45s
Unit tests (macos-13, 3.9)	56s
Unit tests (macos-13, 3.10)	1m 0s
Unit tests (macos-13, 3.11)	49s
Unit tests (macos-13, 3.12)	1m 5s
Unit tests (macos-13, 3.13-dev)	1m 25s
Unit tests (macos-14, 3.10)	29s
Unit tests (macos-14, 3.11)	26s
Unit tests (macos-14, 3.12)	29s
Unit tests (macos-14, 3.13-dev)	43s
	14m 4s

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