Fix implicit-fallthrough compiler warning introduced in 6dda292d4d.

For some reason at least gcc-9 warns about the fallthrough, even
though it otherwise recognizes that elog(ERROR, ...) doesn't return.

Author: Andres Freund

src/backend/utils/adt/jsonb_util.c

@@ -247,8 +247,10 @@ compareJsonbContainers(JsonbContainer *a, JsonbContainer *b)
 						break;
 					case jbvBinary:
 						elog(ERROR, "unexpected jbvBinary value");
+						break;
 					case jbvDatetime:
 						elog(ERROR, "unexpected jbvDatetime value");
+						break;
 				}
 			}
 			else