Avoid parsing error from bogus Azure Flexible Server custom GUC

cmd/postgres_exporter/pg_setting.go

@@ -31,7 +31,7 @@ func querySettings(ch chan<- prometheus.Metric, server *Server) error {
 	//
 	// NOTE: If you add more vartypes here, you must update the supported
 	// types in normaliseUnit() below
-	query := "SELECT name, setting, COALESCE(unit, ''), short_desc, vartype FROM pg_settings WHERE vartype IN ('bool', 'integer', 'real');"
+	query := "SELECT name, setting, COALESCE(unit, ''), short_desc, vartype FROM pg_settings WHERE vartype IN ('bool', 'integer', 'real') AND name != 'sync_commit_cancel_wait';"
 
 	rows, err := server.db.Query(query)
 	if err != nil {