CI: switch to 1.11-nightly for now #13266

Job	Run time
doctest (1.9, ubuntu-latest)	21m 12s
doctest (1.10, ubuntu-latest)	23m 16s
test (1.6, short, ubuntu-latest)	55m 11s
doctest (1.11-nightly, ubuntu-latest)	24m 20s
test (1.6, long, ubuntu-latest)	43m 50s
doctest (1.10, ubuntu-latest, depwarn=error)	22m 30s
test (1.9, short, ubuntu-latest)	51m 58s
doctest (1.10, macOS-14)	12m 11s
test (1.9, long, ubuntu-latest)	39m 30s
test (1.10, short, ubuntu-latest)	44m 30s
test (1.10, long, ubuntu-latest)	37m 47s
test (1.11-nightly, short, ubuntu-latest)	59m 26s
test (1.11-nightly, long, ubuntu-latest)	46m 51s
test (1.10, short, ubuntu-latest, depwarn=error)	42m 25s
test (1.10, long, ubuntu-latest, depwarn=error)	36m 28s
test (1.10, short, macOS-14)	35m 11s
test (1.10, long, macOS-latest)	48m 13s
	10h 44m 49s

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