Include doesn't work with variable expansion

Summary

When global variables are included as part of an include in the .gitlab-ci.yml file, variable expansion doesn't work as expected.

Steps to reproduce

• included.yml

variables:
  x: ${CI_PROJECT_NAME}

• base.yml

include:
- local: 'included.yml'

What is the current bug behavior?

Variable x will not be populated with the CI_PROJECT_NAME predefined variable. Rather it is copied over as a literal string. Escaping the variable with '$$' doesn't work either.

What is the expected correct behavior?

x -> should have whatever $CI_PROJECT_NAME expands to.