Update .gitlab-ci.yml

1 job for master in 17 seconds (queued for 3 seconds)
Name Stage Failure
failed
Test SSH Test
Setting up xauth (1:1.1-0ubuntu1) ...
Processing triggers for libc-bin (2.31-0ubuntu9.2) ...
$ eval $(ssh-agent -s)
Agent pid 470
$ echo "$SSH_PRIVATE_KEY" | base64 -d | tr -d '\r' | ssh-add - > /dev/null
base64: invalid input
Error loading key "(stdin)": invalid format
Cleaning up file based variables
ERROR: Job failed: exit code 1