gitlab ci ERROR: There are no scenarios; must have at least one. code example

Example: yarn ERROR: There are no scenarios; must have at least one.

curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
sudo apt update
sudo apt install yarn