Bump version to 20.3.0 #3318

Job	Run time
Build (ubuntu-latest, x86_64-unknown-linux-gnu, amd64)	2m 28s
Unit tests (ubuntu-20.04, 1.21)	6m 28s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, arm64)	3m 13s
Integration tests (ubuntu-20.04, 1.21, .CLI.)	16m 9s
Unit tests (ubuntu-22.04, 1.21)	6m 35s
Build (macos-latest, x86_64-apple-darwin, amd64)	3m 22s
Integration tests (ubuntu-20.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	13m 41s
Build (macos-latest, aarch64-apple-darwin, arm64)	4m 39s
Integration tests (ubuntu-22.04, 1.21, .CLI.)	14m 51s
Build (windows-latest, x86_64-pc-windows-gnu, amd64)	8m 27s
Integration tests (ubuntu-22.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	13m 14s
	1h 33m 7s

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