Ensure /etc permissions in CI

Due to nodepool being built from the docker image having
permissions to /etc as 0775, ssh certs are failing to authorize
users on metal deployments.

We apply this fix only in CI as presumably this should not happen
on "normal" systems.

Change-Id: I2ea2eb383ca95aa486a3be3ec7d8122e5e2b3294

zuul.d/playbooks/pre-gate-cleanup.yml

@@ -59,6 +59,12 @@
             - rocky-devel.repo
             - rocky-addons.repo
 
+        - name: Ensure /etc has proper permissions
+          ansible.builtin.file:
+            path: /etc
+            mode: "0755"
+            state: directory
+
     - name: Adjust ssh server configuration based on STIG requirements
       vars:
         sshd_settings: