chore: use [sources] in Project.toml #3707

Job	Run time
downgrade	1h 7m 31s
test (1.10, ubuntu-latest, core_layers)	15m 54s
test (1.10, ubuntu-latest, normalize_layers)	14m 1s
test (1.10, ubuntu-latest, recurrent_layers)	20m 32s
test (1.10, ubuntu-latest, autodiff)	24m 7s
test (1.10, ubuntu-latest, misc)	28m 1s
test (1.10, ubuntu-latest, reactant)	10m 45s
test (1, ubuntu-latest, core_layers)	18m 47s
test (1, ubuntu-latest, normalize_layers)	17m 11s
test (1, ubuntu-latest, recurrent_layers)	22m 0s
test (1, ubuntu-latest, autodiff)	24m 23s
test (1, ubuntu-latest, misc)	33m 1s
test (1, ubuntu-latest, reactant)	15m 25s
test (1, macos-latest, all)	3h 25m 59s
test (1, windows-latest, all)	1h 8m 58s
	9h 46m 35s

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