CI: Use a Ubuntu 20.04 container to keep Ubuntu 20.04 support #1970

Job	Run time
build-spidermonkey-win	15s
build-spidermonkey-unix (macos-14, 3.10)	8s
build-spidermonkey-unix (macos-13, 3.10)	9s
build-spidermonkey-unix (ubuntu-22.04, 3.10)	8s
sdist	30s
build-spidermonkey-unix (ubuntu-22.04-arm, 3.10)	8s
build-and-test (ubuntu-22.04, 3.11)	1m 24s
build-and-test (ubuntu-22.04, 3.9)	1m 43s
build-and-test (ubuntu-22.04, 3.8)	1m 38s
build-and-test (ubuntu-22.04, 3.10)	1m 38s
build-and-test (ubuntu-22.04, 3.12)	1m 21s
build-and-test (macos-13, 3.9)	1s
build-and-test (ubuntu-22.04, 3.13)	1m 38s
build-and-test (macos-13, 3.11)	1s
build-and-test (macos-13, 3.10)	2m 47s
build-and-test (macos-13, 3.8)	1s
build-and-test (macos-13, 3.12)	2m 57s
build-and-test (macos-13, 3.13)	1s
build-and-test (macos-14, 3.8)	2m 59s
build-and-test (macos-14, 3.9)	2m 52s
build-and-test (macos-14, 3.12)	2m 38s
build-and-test (macos-14, 3.13)	1s
build-and-test (windows-2022, 3.8)	2m 49s
build-and-test (windows-2022, 3.9)	2m 50s
build-and-test (windows-2022, 3.13)	1m 24s
build-and-test (macos-14, 3.11)	1s
build-and-test (ubuntu-22.04-arm, 3.9)	2m 45s
build-and-test (macos-14, 3.10)	1s
build-and-test (ubuntu-22.04-arm, 3.12)	1m 17s
build-and-test (windows-2022, 3.10)	2m 49s
build-and-test (ubuntu-22.04-arm, 3.8)	2m 44s
build-and-test (ubuntu-22.04-arm, 3.13)	2m 50s
build-and-test (windows-2022, 3.12)	2m 49s
build-and-test (windows-2022, 3.11)	2m 49s
build-and-test (ubuntu-22.04-arm, 3.10)	1m 13s
build-and-test (ubuntu-22.04-arm, 3.11)	2m 44s
publish-nightly	1s
publish	1s
publish-archive	1s
	54m 6s

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