Bump pyo3-build-config from 0.20.3 to 0.21.0 #4320

Job	Run time
Check for upstream trigger phrase	2s
Test importing with bare requirements	12m 54s
Build & Test (ubuntu-latest, python: 3.9, distributed: false)	8m 29s
Build & Test (ubuntu-latest, python: 3.10, distributed: false)	8m 54s
Build & Test (ubuntu-latest, python: 3.11, distributed: false)	8m 39s
Build & Test (ubuntu-latest, python: 3.12, distributed: false)	9m 4s
Build & Test (windows-latest, python: 3.9, distributed: false)	15m 2s
Build & Test (windows-latest, python: 3.10, distributed: false)	16m 33s
Build & Test (windows-latest, python: 3.11, distributed: false)	16m 56s
Build & Test (windows-latest, python: 3.12, distributed: false)	17m 32s
Build & Test (macos-latest, python: 3.9, distributed: false)	25m 1s
Build & Test (macos-latest, python: 3.10, distributed: false)	11m 40s
Build & Test (macos-latest, python: 3.11, distributed: false)	19m 20s
Build & Test (macos-latest, python: 3.12, distributed: false)	16m 14s
Build & Test (ubuntu-latest, python: 3.9, distributed: true)	11m 2s
Build & Test (ubuntu-latest, python: 3.11, distributed: true)	9m 6s
	3h 26m 28s

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