Bump version to 20.3.0 #3326

Job	Run time
Unit tests (ubuntu-20.04, 1.21)	5m 55s
Unit tests (ubuntu-22.04, 1.21)	6m 15s
Build (ubuntu-latest, x86_64-unknown-linux-gnu, amd64)	2m 43s
Build (ubuntu-latest, aarch64-unknown-linux-gnu, arm64)	3m 18s
Build (macos-latest, x86_64-apple-darwin, amd64)	7m 53s
Build (macos-latest, aarch64-apple-darwin, arm64)	5m 37s
Build (windows-latest, x86_64-pc-windows-gnu, amd64)	8m 43s
Integration tests (ubuntu-20.04, 1.21, .CLI.)	15m 41s
Integration tests (ubuntu-20.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	13m 21s
Integration tests (ubuntu-22.04, 1.21, .CLI.)	15m 4s
Integration tests (ubuntu-22.04, 1.21, ^Test(([^C])\|(C[^L])\|(CL[^I])).*$)	13m 10s
	1h 37m 40s

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