Anchor does not work for global cache

GitLab CI/CD
1

I tried to use an anchor for a global cache definition but got the following error:
This GitLab CI configuration is invalid: jobs:build:cache config contains unknown keys: <<

Why does anchor not work in this case?

default:
    cache: &global_cache
    - key: "$CI_COMMIT_REF_NAME"
      policy: pull
      paths:
        - build
    - key:
        files:
          - gradle/wrapper/gradle-wrapper.properties
      policy: pull          
      paths: 
        - .gradle/wrapper
        - .gradle/notifications   
 
build:
  cache:
    <<: *global_cache
    policy: push
  stage: build
  script: ./gradlew --build-cache  assemble
...

Thanks

2

Because it’s not supported.