Update alphadecays.txt #8279

Job	Run time
classicmode_1d_3dgrid	4m 13s
classicmode_3d	7m 40s
kilonova_1d_1dgrid	4m 48s
kilonova_1d_3dgrid	5m 55s
kilonova_2d_2dgrid	8m 22s
kilonova_2d_2dgrid_barnesthermalisation	5m 40s
kilonova_2d_2dgrid_expansionopac	4m 56s
kilonova_2d_2dgrid_xcomgammaphotoion	5m 13s
kilonova_2d_3dgrid	7m 6s
nebular_1d_3dgrid	11m 55s
nebular_1d_3dgrid_limitbfest	14m 4s
combine_checksums	56s
	1h 20m 48s

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