preflight: fix structure of _ceph_repo

This is a legacy becasue the first intent was to make
a list with multiple repos but this variable now needs to be a dict.

Signed-off-by: Guillaume Abrioux <gabrioux@Guillaumes-MacBook-Pro.local>
(cherry picked from commit 6ab8913)

cephadm-preflight.yml

@@ -56,10 +56,10 @@
         - name: set_fact _ceph_repo
           set_fact:
             _ceph_repo:
-              - name: ceph_stable
-                description: "{{ 'Ceph Stable repo' if ceph_origin == 'community' else 'IBM Ceph repo' }}"
-                rpm_key: "{{ ceph_stable_key if ceph_origin == 'community' else ceph_ibm_key }}"
-                baseurl: "{{ ceph_community_repo_baseurl if ceph_origin == 'community' else ceph_ibm_repo_baseurl }}"
+              name: ceph_stable
+              description: "{{ 'Ceph Stable repo' if ceph_origin == 'community' else 'IBM Ceph repo' }}"
+              rpm_key: "{{ ceph_stable_key if ceph_origin == 'community' else ceph_ibm_key }}"
+              baseurl: "{{ ceph_community_repo_baseurl if ceph_origin == 'community' else ceph_ibm_repo_baseurl }}"
 
         - name: configure ceph community repository stable key
           rpm_key: