.gitlab-ci.yml: correct syntax

20 jobs for master in 49 minutes and 50 seconds (queued for 24 minutes and 7 seconds)
Status Job ID Name Coverage
  Stage0
passed #4981
pull base distributions

00:00:27

 
  Stage1
passed #4986
base:10

00:07:40

passed #4987
base:16.04

00:00:12

passed #4988
base:16.10

00:00:13

passed #4984
base:8

00:00:11

passed #4985
base:9

00:05:39

passed #4982
docker-builder

00:00:56

passed #4983
proxy

00:00:44

 
  Stage2
passed #4989
base:8-backports

00:01:23

passed #4990
dune:2.3

00:00:52

passed #4991
dune:2.4

00:00:44

passed #4992
dune:2.5

00:00:27

passed #4993
dune:2.6

00:12:31

passed #4994
dune:git

00:09:21

 
  Stage3
passed #4995
dune-fufem:2.4

00:03:26

passed #4996
dune-fufem:git

00:03:48

passed #4997
dune-pdelab-deps:2.6

00:02:28

passed #4998
dune-pdelab-deps:git

00:02:07

 
  Publish
passed #5000
publish

00:12:27

failed #4999
publish

00:55:04