Bump one CI config to ubuntu-24.04 #311

Job	Run time
build (Debug, yes, 3.12, yes, ubuntu-24.04, gcc -v)	58s
build (Debug, yes, 3.11, yes, ubuntu-20.04, gcc)	3m 24s
build (Debug, yes, 3.10, yes, ubuntu-20.04, gcc)	3m 20s
build (Debug, yes, 3.9, yes, ubuntu-20.04, gcc)	3m 18s
build (Release, 3.8, yes, ubuntu-20.04, gcc)	4m 41s
build (Release, 3.8, yes, gmpxx, no, ubuntu-20.04, gcc)	4m 38s
build (Release, 3.8, yes, ubuntu-20.04, gcc)	4m 27s
build (Release, yes, 3.8, ubuntu-20.04, gcc)	4m 34s
build (Release, 3.9, yes, ubuntu-20.04, gcc)	4m 44s
build (Release, 3.9, yes, flint, yes, ubuntu-20.04, gcc)	4m 35s
build (Debug, 3.8, yes, yes, ubuntu-20.04, clang)	3m 14s
build (Release, 3.8, yes, ubuntu-20.04, clang)	4m 6s
build (Debug, 3.10, yes, 14, yes, boostmp, -k "not integer_nthroot", ubuntu-22.04, deb http://apt...	5m 30s
build (Debug, 3.8, yes, 5, macos-latest, clang)	9m 13s
build (Release, 3.9, no, macos-latest, clang)	9m 22s
build (Debug, 3.8, no, macos-latest, gcc)	10m 34s
build (Release, 3.8, macos-latest, gcc)	19m 36s
build (Release, 3.8, ubuntu-20.04, yes, yes, yes, yes, yes, flint, yes, gcc)	4m 47s
	1h 45m 1s

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