Update .gitlab-ci.yml file

2 jobs for master in 23 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #422500
centos7

00:00:04

passed #422499
ubuntu20.04

00:00:23

 
Name Stage Failure
failed
centos7 Build There has been a runner system failure, please try again
Running with gitlab-runner 13.12.0 (7a6612da)
on ccosvms0006@gitlab.in2p3.fr FxoAW2ya
Preparing the "docker" executor
Using Docker executor with image centos7 ...
Pulling docker image centos7 ...
WARNING: Failed to pull image with policy "always": repository docker.io/centos7 not found: does not exist or no pull access (manager.go:205:2s)
ERROR: Job failed (system failure): failed to pull image "centos7" with specified policies [always]: repository docker.io/centos7 not found: does not exist or no pull access (manager.go:205:2s)