fix yaml syntax

1 job for ci in 1 minute and 33 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #34232
docker
build-centos7

00:01:33

 
Name Stage Failure
failed
build-centos7 Build
Running with gitlab-runner 13.5.0 (ece86343)
on WASP Runner Manager PNU5FWJz
Preparing the "docker+machine" executor
Using Docker executor with image registry.orfeo-toolbox.org/gpasero/wasp/wasp-env-centos7:ci ...
Pulling docker image gitlab/gitlab-runner-helper:x86_64-ece86343 ...
Using docker image sha256:24740ef68ef3be12247abd72bc375847bec0874eab55b8f6e605271cf4fed25b for gitlab/gitlab-runner-helper:x86_64-ece86343 with digest gitlab/gitlab-runner-helper@sha256:2e5b39adb72ccd8695abea4ce0295728712609982cbacb8a6f479a273c047259 ...
Authenticating with credentials from job payload (GitLab Registry)
Pulling docker image registry.orfeo-toolbox.org/gpasero/wasp/wasp-env-centos7:ci ...
ERROR: Job failed: Error response from daemon: manifest for registry.orfeo-toolbox.org/gpasero/wasp/wasp-env-centos7:ci not found: manifest unknown: manifest unknown (docker.go:142:0s)