gitlab-ci.yaml anchor concatenation in script or after_script

Description

It is not possible to use multiple anchors to construct scripts or after_scripts. This would come in very handy in constructing more complex scripts without code duplication.

My Idea is to use a .gitlab.yaml like this:

.echo_foo_after-script: &foo
- echo foo

.echo_bar_after-script: &bar
-  echo bar
  
test1:
  script:
  - do_some_thing
  after_script:
    <<: *foo

test2:
  script:
  - do_some_thing_else
  after_script:
    <<: [*foo, *bar]

For test2 echo_foo_after-script and echo_bar_after-script schould be executed in the order they are called. And for test1 it is just echo_foo_after-script.

At the moment you will end up in a Syntax error like this: Error: jobs:unidirectional_communication:after_script config should be an array of strings

Or is there already a way to do this ?