GitLab CI/CD is replacing file variable content

Summary

When I create a file variable on a project's CI/CD settings, GitLab is replacing any $foo string inside the file with the value of foo variable.

Steps to reproduce

Open a project's CI/CD settings page and create the following variable:

• Name: my_php_file
• Type: File

Variable value:

<?php
trait FooConfig
{
    protected static $foo;
}

Create the .gitlab-ci.yml file on the project repository:

test:
  script: cat $my_php_file

Example Project

https://gitlab.com/adarlan/file-variable-bug

What is the current bug behavior?

GitLab-CI is replacing the $foo string inside the file with the value of foo variable.

So the cat output is:

<?php
trait FooConfig
{
    protected static ;
}

What is the expected correct behavior?

GitLab-CI should not replace anything inside the file. The file content is supposed to be static.

So the cat output should be:

<?php
trait FooConfig
{
    protected static $foo;
}

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's tough to read otherwise.)

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:env:info)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)