Ignore retcode when formatting highstate output

Fixes saltstack#33915.

salt/output/highstate.py

@@ -131,7 +131,15 @@ def output(data):
         data = data.pop('data')
 
     for host, hostdata in six.iteritems(data):
+        if not isinstance(hostdata, dict):
+            # Highstate return data must be a dict, if this is not the case
+            # then this value is likely a retcode.
+            continue
         return _format_host(host, hostdata)[0]
+    log.error(
+        'Data passed to highstate outputter is not a valid highstate return: %s',
+        data
+    )
 
 
 def _format_host(host, data):