Bump tox from 4.20.0 to 4.21.2 #1251

Job	Run time
Check towncrier / Towncrier Checks	25s
Package Rubicon-ObjC / Create Python Package	22s
Pre-commit checks / Pre-commit Checks	21s
Unit tests (macos-12, 3.8)	43s
Unit tests (macos-12, 3.9)	41s
Unit tests (macos-12, 3.10)	42s
Unit tests (macos-12, 3.11)	39s
Unit tests (macos-12, 3.12)	46s
Unit tests (macos-12, 3.13-dev)	1m 33s
Unit tests (macos-13, 3.8)	46s
Unit tests (macos-13, 3.9)	46s
Unit tests (macos-13, 3.10)	1m 4s
Unit tests (macos-13, 3.11)	46s
Unit tests (macos-13, 3.12)	44s
Unit tests (macos-13, 3.13-dev)	1m 21s
Unit tests (macos-14, 3.10)	26s
Unit tests (macos-14, 3.11)	26s
Unit tests (macos-14, 3.12)	35s
Unit tests (macos-14, 3.13-dev)	43s
	13m 49s

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