CI: Use a Ubuntu 20.04 container to keep Ubuntu 20.04 support #1975

Job	Run time
sdist	36s
build-spidermonkey-win	11s
build-spidermonkey-unix (ubuntu-22.04-arm, 3.10)	23s
build-spidermonkey-unix (macos-14, 3.10)	8s
build-spidermonkey-unix (macos-13, 3.10)	8s
build-spidermonkey-unix (ubuntu-22.04, 3.10)	8s
build-and-test (ubuntu-22.04, 3.10)	1m 44s
build-and-test (ubuntu-22.04, 3.8)	1m 50s
build-and-test (ubuntu-22.04, 3.9)	1m 52s
build-and-test (ubuntu-22.04, 3.12)	1m 46s
build-and-test (macos-13, 3.8)	5m 18s
build-and-test (macos-13, 3.9)	4m 13s
build-and-test (macos-13, 3.11)	4m 7s
build-and-test (macos-13, 3.13)	6m 20s
build-and-test (macos-13, 3.10)	4m 2s
build-and-test (macos-13, 3.12)	4m 56s
build-and-test (macos-14, 3.8)	3m 20s
build-and-test (ubuntu-22.04, 3.11)	1m 48s
build-and-test (macos-14, 3.9)	3m 27s
build-and-test (macos-14, 3.10)	2m 41s
build-and-test (ubuntu-22.04, 3.13)	1m 52s
build-and-test (macos-14, 3.12)	2m 29s
build-and-test (windows-2022, 3.10)	8m 0s
build-and-test (macos-14, 3.11)	2m 43s
build-and-test (windows-2022, 3.8)	7m 18s
build-and-test (macos-14, 3.13)	2m 29s
build-and-test (windows-2022, 3.11)	8m 2s
build-and-test (windows-2022, 3.9)	7m 18s
build-and-test (ubuntu-22.04-arm, 3.8)	3m 20s
build-and-test (windows-2022, 3.12)	7m 9s
build-and-test (windows-2022, 3.13)	7m 10s
build-and-test (ubuntu-22.04-arm, 3.12)	3m 21s
build-and-test (ubuntu-22.04-arm, 3.9)	4m 34s
build-and-test (ubuntu-22.04-arm, 3.11)	3m 48s
build-and-test (ubuntu-22.04-arm, 3.10)	4m 17s
build-and-test (ubuntu-22.04-arm, 3.13)	3m 23s
publish-nightly	1s
publish	1s
publish-archive	1s
	2h 6m 14s

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