CI: switch ubuntu-20.04 to ubuntu-22.04 #6108

Job	Run time
Test in OpenBSD	8m 29s
testinstall - - ubuntu-latest	4m 57s
Cross compiler for s390x	29m 17s
teststandard - - ubuntu-latest	20m 50s
testmanuals - - ubuntu-latest	6m 0s
testexpect testmockpkg testspecial test-compile testlibgap testkernel testworkspace - - ubuntu-latest	6m 56s
testpackages testinstall-loadall - - ubuntu-latest	26m 12s
makemanuals testmakeinstall - CONFIGFLAGS="--prefix=/tmp/gapprefix" NO_COVERAGE=1 - ubuntu-latest	6m 18s
teststandard - ABI=32 CONFIGFLAGS="" - ubuntu-22.04	19m 21s
testinstall - HPCGAP=yes ABI=64 - ubuntu-latest	7m 30s
testmockpkg testinstall testworkspace - BOOTSTRAP_MINIMAL=yes - macos-latest	5m 49s
testbugfix - CONFIGFLAGS="--enable-memory-checking" - ubuntu-latest	27m 48s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=64 BUILDDIR=out-of-tree CONFIGFLAGS="--enable-valgrind" - ubuntu-latest	4m 33s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=32 BUILDDIR=out-of-tree CONFIGFLAGS="" - ubuntu-22.04	4m 50s
testinstall - JULIA=yes CONFIGFLAGS="--enable-debug" - ubuntu-22.04	5m 22s
testmockpkg testinstall - - windows-2019	15m 12s
Send Slack notification on status change	4s
	3h 19m 28s

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