Only log an error for is_rfc vs canonical_name mismatch for Document objects - it's OK for DocHistory to have the mismatch given how DocHistory computes is_rfc()

 - Legacy-Id: 18903

Author: rjsparks

ietf/doc/models.py

@@ -371,7 +371,8 @@ def rfc_number(self):
                 if n.startswith("rfc"):
                     self._cached_rfc_number = n[3:]
                 else:
-                    logger.error("Document self.is_rfc() is True but self.canonical_name() is %s" % n)
+                    if isinstance(self,Document):
+                        logger.error("Document self.is_rfc() is True but self.canonical_name() is %s" % n)
         return self._cached_rfc_number
 
     @property