Update alphadecays.txt #8284

Job	Run time
classicmode_1d_3dgrid	4m 24s
classicmode_3d	7m 59s
kilonova_1d_1dgrid	4m 56s
kilonova_1d_3dgrid	4m 55s
kilonova_2d_2dgrid	6m 45s
kilonova_2d_2dgrid_barnesthermalisation	5m 41s
kilonova_2d_2dgrid_expansionopac	4m 54s
kilonova_2d_2dgrid_xcomgammaphotoion	5m 35s
kilonova_2d_3dgrid	7m 11s
nebular_1d_3dgrid	11m 31s
nebular_1d_3dgrid_limitbfest	13m 56s
combine_checksums	28s
	1h 18m 15s

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