build: drop support for Python 3.9 #1838

Job	Run time
Build slim tarball	1m 30s
x86_64-darwin: with shared libraries	41m 53s
x86_64-linux: with shared libraries	28m 54s
aarch64-linux: with shared libraries	24m 53s
aarch64-darwin: with shared libraries	22m 0s
	1h 59m 10s

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