Re-enable ownership of checked-out files in CI pipeline

Fixes the pipeline by re-enabling write support for the checked out files. To be investigated how to fix the issu another time (cc @crbaldi).

.gitlab-ci.yml

@@ -15,6 +15,9 @@ variables:
     name: gitlab-registry.cern.ch/acc-co/docker/acc-base-images/acc_cc7@sha256:bde86612d325a8090c0a7d270efb56702983fc6d41d1b57a4f26ed0342cc1c64
     # Default to a non-root user ('runner-user') who is in the special "wheel" group, so can run root commands with su -c "{command}".
     entrypoint: [ '/bin/bash', '-c', '/sbin/useradd -G wheel runner-user && sed -i -E "s/\#(auth\s.*)/\1/" /etc/pam.d/su && exec /bin/su runner-user -c /bin/bash' ]
+  variables:
+    # https://docs.gitlab.com/runner/configuration/feature-flags.html#available-feature-flags
+    FF_DISABLE_UMASK_FOR_DOCKER_EXECUTOR: 0
 
 
 .dev_test_base: