deployment from gitlab-ci with password protected ssh private key file

gistfile1.txt

deploy to staging:
  image: ${CI_DEPENDENCY_PROXY_DIRECT_GROUP_IMAGE_PREFIX}/alpine:3.17.2
  stage: deploy
  before_script:
    - "apk add openssh-client"
    - eval $(ssh-agent -s)
    - mkdir -p ~/.ssh
    - chmod 700 ~/.ssh
    - echo '#!/bin/sh' > ~/.ssh/tmp
    - echo 'echo $SSH_PRIV_KEY_PASS' >> ~/.ssh/tmp && chmod 700 ~/.ssh/tmp
    - echo "$SSH_PRIVATE_KEY" | base64 -d | tr -d '\r' | DISPLAY=None SSH_ASKPASS=~/.ssh/tmp ssh-add -
    - echo -e "Host *\n\tStrictHostKeyChecking no\n\n" >> ~/.ssh/config
  script:
    - ssh <myuser>@<myserver> "docker service update --image $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG <myproject>"
  when: manual

the $SSH_PRIVATE_KEY CI variable has to be base64 encoded