add ssh.git.shackspace.de server keys via variable

avoid some weird rate limiting which is in place

.gitlab-ci.yml

@@ -8,7 +8,7 @@ before_script:
   # prepare git fetching of secrets
   - echo "$gitlab_deploy_privkey" > ~/.ssh/gitlab_deploy.key
   - chmod 600 ~/.ssh/gitlab_deploy.key
-  - ssh-keyscan -H 'ssh.git.shackspace.de' >> ~/.ssh/known_hosts
+  - echo "$ssh_git_shackspace_serverkey" >> ~/.ssh/known_hosts
   # import secret key for secrets
   - echo "$secrets_gpg_key" | gpg --import
 deployment test: