change rc tag name #426

Job	Run time
docker (DIR=master)	9m 11s
docker (DIR=master VARIANT=alpine)	6m 56s
docker (DIR=28)	4m 11s
docker (DIR=28 VARIANT=slim)	3m 10s
docker (DIR=28 VARIANT=alpine)	3m 37s
docker (DIR=27)	3m 42s
docker (DIR=27 VARIANT=slim)	2m 50s
docker (DIR=27 VARIANT=alpine)	3m 5s
docker (DIR=26)	12m 32s
docker (DIR=26 VARIANT=slim)	7m 3s
docker (DIR=26 VARIANT=alpine)	7m 41s
docker (DIR=25)	11m 6s
docker (DIR=25 VARIANT=slim)	6m 14s
docker (DIR=25 VARIANT=alpine)	6m 53s
docker (DIR=24)	9m 28s
docker (DIR=24 VARIANT=slim)	5m 40s
docker (DIR=24 VARIANT=alpine)	6m 34s
	1h 49m 53s

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