ci: failfast in case of conflicts (#16777)

.github/helper/install_dependencies.sh

@@ -2,6 +2,13 @@
 
 set -e
 
+# Check for merge conflicts before proceeding
+python -m compileall -f "${GITHUB_WORKSPACE}"
+if grep -lr --exclude-dir=node_modules "^<<<<<<< " "${GITHUB_WORKSPACE}"
+    then echo "Found merge conflicts"
+    exit 1
+fi
+
  # install wkhtmltopdf
 wget -O /tmp/wkhtmltox.tar.xz https://github.com/frappe/wkhtmltopdf/raw/master/wkhtmltox-0.12.3_linux-generic-amd64.tar.xz
 tar -xf /tmp/wkhtmltox.tar.xz -C /tmp