fix: chmod 600 SSH signing key before use

GitLab runner writes file-type CI variables with 0666 permissions.
ssh-keygen refuses to use a private key that is world-readable,
causing git commit signing to fail.

Signed-off-by: Jose Angel Morena <jmorenas@redhat.com>

Author: jangel97

entrypoint.sh

@@ -48,6 +48,7 @@ fi
 
 # Configure git commit signing
 if [ -n "${GIT_SSH_SIGNING_KEY:-}" ]; then
+  chmod 600 "$GIT_SSH_SIGNING_KEY"
   git config --global gpg.format ssh
   git config --global user.signingkey "$GIT_SSH_SIGNING_KEY"
   git config --global commit.gpgsign true