How to use personal github access token with gitlab runner

I mirrored Github repository from Github to run builds with gitlab runner. My project has private gems hosted on Github and when the build is failing with

Fetching git@github.com:private/gem.git
Host key verification failed.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

Retrying `git clone 'git@github.com:private/gem.git' "/builds-ci/gitlab/repo/vendor/ruby/2.4.0/cache/bundler/git/gem-a356dd016736a58b8b77677e8d7df689f8f43ada" --bare --no-hardlinks --quiet` due to error (2/4): Bundler::Source::Git::GitCommandError Git error: command `git clone 'git@github.com:private/gem.git' "/builds/gitlab-ci/repo/vendor/ruby/2.4.0/cache/bundler/git/gem-a356dd016736a58b8b77677e8d7df689f8f43ada" --bare --no-hardlinks --quiet` in directory /builds/gitlab-ci/repo has failed.Host key verification failed.
fatal: Could not read from remote repository.

I used personal github access token to mirror private repositories from Github to Gitlab. There is a way to use github access token to clone private gems with bundler:

export BUNDLE_GITHUB__COM=x-access-token:<token>

Do I need to create a separate access token and paste it into .gitlab-ci.yml

image: ruby:2.4.1

variables:
  BUNDLE_GITHUB__COM=x-access-token:<token>

...

Or I can use the token which I used to mirror repositories from Github? Like this

variables:
  BUNDLE_GITHUB__COM=x-access-token:$SOME_GITLAB_JOB_ACCESS_TOKEN

?