Fix unauth_psql detection on other protocols

If the protocol we send the request to reflects our message we detect it
as a FP. Excluding a 500 error code should be a more general rule.

network/misconfig/unauth-psql.yaml

@@ -37,8 +37,10 @@ tcp:
         condition: and
 
       - type: word
+        part: raw
         words:
           - "FTP"
           - "HTTP"
+          - "500"
         condition: or
         negative: true