fix: Just drop the registry reference in URL for latest image

This simplifies the retrieval of the URL we pass to Skopeo by just
dropping the registry and retaining the rest of the URL

src/ublue_update/update_checks/system.py

@@ -23,22 +23,18 @@ def system_update_check():
     """Parse installation digest and image"""
     deployments = loads(out)["deployments"][0]
     installation_digest = deployments["base-commit-meta"]["ostree.manifest-digest"]
-    current_image = deployments["container-image-reference"].split(":")
+    current_image = deployments["container-image-reference"].split(":", 1)
 
     """Dissect current image to form URL to latest image"""
     protocol = "docker://"
     url = current_image[1]
-    tag = current_image[2]
 
-    """Shift when image contains protocol"""
-    if url in protocol:
-        protocol = current_image[1] + ":"
-        url = current_image[2]
-        tag = current_image[3]
+    """Add protocol if URL doesn't contain it"""
+    if protocol not in url:
+        url = protocol + url
 
     """Pull digest from latest image"""
-    latest_image = protocol + url + ":" + tag
-    latest_digest = skopeo_inspect(latest_image)
+    latest_digest = skopeo_inspect(url)
 
     """Compare current digest to latest digest"""
     if installation_digest == latest_digest: