Syntax error when adding SSH key in before_script section

Reference: https://gitlab.ida.liu.se/help/ci/ssh_keys/README.md

The following script has problems. Even though I changed the last symbol from ` to ' , the error is as follow:

$ ssh-add <(echo "$SSH_PRIVATE_KEY") /bin/sh: eval: line 24: syntax error: unexpected "("

Does anyone have the same issue here ?

before_script:
  # Install ssh-agent if not already installed, it is required by Docker.
  # (change apt-get to yum if you use a CentOS-based image)
  - 'which ssh-agent || ( apt-get update -y && apt-get install openssh-client -y )'

  # Run ssh-agent (inside the build environment)
  - eval $(ssh-agent -s)

  # Add the SSH key stored in SSH_PRIVATE_KEY variable to the agent store
  - ssh-add <(echo "$SSH_PRIVATE_KEY")

  # For Docker builds disable host key checking. Be aware that by adding that
  # you are suspectible to man-in-the-middle attacks.
  # WARNING: Use this only with the Docker executor, if you use it with shell
  # you will overwrite your user's SSH config.
  - mkdir -p ~/.ssh
  - '[[ -f /.dockerinit ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config`