Bump pyo3 from 0.20.2 to 0.21.0 #133

Job	Run time
windows (x64)	59s
linux-cross (aarch64)	1m 20s
macos	45s
windows (x86)	1m 3s
linux (x86_64)	1m 8s
linux-cross (armv7)	1m 20s
linux (i686)	1m 13s
linux-cross (s390x)	1m 19s
musllinux (x86_64-unknown-linux-musl)	55s
musllinux-cross (aarch64-unknown-linux-musl, aarch64)	50s
linux-cross (ppc64le)	1m 17s
musllinux (i686-unknown-linux-musl)	59s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	48s
linux-cross (ppc64)	1m 20s
Release	0s
	15m 16s

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