Use different method to modify known hosts

.gitlab-ci.yml

@@ -5,9 +5,13 @@ stages:
 .setup-ssh-euxfel-gitlab: &setup-ssh-euxfel-gitlab
   - eval $(ssh-agent -s)
   - echo "$SSH_PRIVATE_KEY_GITLAB" | tr -d '\r' | ssh-add -
-  - mkdir -p ~/.ssh
-  - chmod 700 ~/.ssh
-  - ssh-keyscan -p 10022 git.xfel.eu > ~/.ssh/known_hosts
+  #  Our self-hosted runners have persistent home directories, so here we store
+  #  the known_hosts file in the temporary project dir and tell git to use a ssh
+  #  command that uses this hosts file during operations
+  - export GIT_SSH_COMMAND="ssh UserKnownHostsFile=$CI_PROJECT_DIR/.ssh/known_hosts"
+  - mkdir -p $CI_PROJECT_DIR/.ssh
+  - chmod 700 $CI_PROJECT_DIR/.ssh
+  - ssh-keyscan -p 10022 git.xfel.eu > $CI_PROJECT_DIR/.ssh/known_hosts
 
 checks:
   stage: check
@@ -31,6 +35,8 @@ pytest:
   only: [merge_requests]
   before_script:
     - *setup-ssh-euxfel-gitlab
+    - ls  $CI_PROJECT_DIR/.ssh
+    - echo $GIT_SSH_COMMAND
   script:
     - python3 -m venv .venv
     - source .venv/bin/activate