Let's try to do it with a file on disk

.forgejo/workflows/deploy.yml

@@ -14,11 +14,9 @@ jobs:
           bundle config set path vendor/bundle
           bundle install --jobs=4 --retry=3
           command -v rsync >/dev/null || ( apt-get update -y && apt-get install rsync -y )
-          command -v ssh-agent >/dev/null || ( apt-get update -y && apt-get install openssh-client -y )
-          eval $(ssh-agent -s)
-          echo "$SSH_PRIVATE_KEY" | tr -d '\r' | ssh-add -
           mkdir -p ~/.ssh
           chmod 700 ~/.ssh
+          echo "$SSH_PRIVATE_KEY" >~/.ssh/id_ed25519
           echo "$SSH_KNOWN_HOSTS" > ~/.ssh/known_hosts
           chmod 644 ~/.ssh/known_hosts
       - name: "Deploy"