fix(infra): lob-backtest-sweep chmod 600 ~/.ssh/config

The template wrote ~/.ssh/config but didn't chmod it. OpenSSH refused
the file with 'Bad owner or permissions on /root/.ssh/config' and the
git clone failed with 'exit status 128' before fxt-backtest could
compile.

Same one-line fix that alpha-perception-template.yaml has had since
forever. Verified: lob-backtest-sweep-<new> ensure-binary now passes
the SSH check and starts cargo build.

infra/k8s/argo/lob-backtest-sweep-template.yaml

@@ -183,6 +183,7 @@ spec:
             cp /etc/git-ssh/ssh-privatekey ~/.ssh/id_ed25519
             chmod 600 ~/.ssh/id_ed25519
             printf 'Host *\n  StrictHostKeyChecking no\n  UserKnownHostsFile /dev/null\n' > ~/.ssh/config
+            chmod 600 ~/.ssh/config
 
             REPO="ssh://git@gitlab-gitlab-shell.foxhunt.svc.cluster.local:2222/root/foxhunt.git"
             BUILD="/cargo-target/src"