make 28 as latest #439

Job	Run time
docker (DIR=master)	9m 13s
docker (DIR=master VARIANT=alpine)	6m 47s
docker (DIR=28)	4m 11s
docker (DIR=28 VARIANT=slim)	3m 1s
docker (DIR=28 VARIANT=alpine)	3m 27s
docker (DIR=27)	3m 49s
docker (DIR=27 VARIANT=slim)	2m 53s
docker (DIR=27 VARIANT=alpine)	3m 4s
docker (DIR=26)	12m 27s
docker (DIR=26 VARIANT=slim)	7m 3s
docker (DIR=26 VARIANT=alpine)	7m 28s
docker (DIR=25)	11m 4s
docker (DIR=25 VARIANT=slim)	6m 2s
docker (DIR=25 VARIANT=alpine)	6m 39s
docker (DIR=24)	9m 36s
docker (DIR=24 VARIANT=slim)	5m 45s
docker (DIR=24 VARIANT=alpine)	6m 29s
	1h 48m 58s

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