os_images: rc assert fix

Author: bbezak

roles/os_images/tasks/prechecks.yml

@@ -10,7 +10,7 @@
 - name: Display warning message about the container engine
   ansible.builtin.assert:
     that:
-      - result.rc = 0
+      - result.rc == 0
     fail_msg: >
       Container runtime engine could not be found - make sure it is installed.
       Elements that depend on it will likely fail when building.