Improper script in example on 'Keyword reference for the .gitlab-ci.yml file' page

Description

There is a simple mistake in the second example of the Complete example for release section on Keyword reference for the .gitlab-ci.yml file page.

Link to that section: https://docs.gitlab.com/ee/ci/yaml/#complete-example-for-release

The script within release_job:

  script:
    - echo 'running release_job for $TAG'

uses apostrophe while having a variable referenced inside and due to that the variable will not be resolved properly. Using quotation marks is required for that purpose (and it is properly used in the rest of the examples).