fix yaml syntax in compose files with multiple yaml anchors

Starting with compose version 2.17, yaml parsing has become more strict and the formerly accepted but invalid syntax to define multiple yaml anchors is now rejected.

To apply the fix manually, replace:

 environment:
      << : *envs-anchor-1
      << : *envs-anchor-2

with:

    environment:
      << : [*envs-anchor-1, *envs-anchor-2]

(CMS-22995)