fix: update contents of the policy.yml.example file

The contents of the file were based on the initial RFC format, which was
then changed.

Signed-off-by: Flavio Castelli <fcastelli@suse.com>

Author: flavio

policies.yml.example

@@ -8,22 +8,22 @@ psp-capabilities:
     required_drop_capabilities: ["KILL"]
 pod-image-signatures: # policy group
   policies:
-    - name: sigstore_pgp
+    sigstore_pgp:
       url: ghcr.io/kubewarden/policies/verify-image-signatures:v0.2.8
       settings:
         signatures:
           - image: "*"
             pubKeys:
               - "-----BEGIN PUBLIC KEY-----xxxxx-----END PUBLIC KEY-----"
               - "-----BEGIN PUBLIC KEY-----xxxxx-----END PUBLIC KEY-----"
-    - name: sigstore_gh_action
+    sigstore_gh_action:
       url: ghcr.io/kubewarden/policies/verify-image-signatures:v0.2.8
       settings:
         signatures:
           - image: "*"
             githubActions:
             owner: "kubewarden"
-    - name: reject_latest_tag
+    reject_latest_tag:
       url: ghcr.io/kubewarden/policies/trusted-repos-policy:v0.1.12
       settings:
         tags: