Set default merge strategy so it doesn't hiccup

see https://github.com/rse-ops/docker-images/runs/3970684205?check_suite_focus=true

docker-images/deploy.sh

@@ -11,6 +11,7 @@ fi
 printf "GitHub Actor: ${GITHUB_ACTOR}\n"
 git config --global user.name "github-actions"
 git config --global user.email "github-actions@users.noreply.github.com"
+git config pull.rebase false
 
 # Clone GitHub pages branch with site
 git clone -b ${branch} https://github.com/${GITHUB_REPOSITORY}.git /tmp/repo