Fix combine with session config (#14139)

* fix combine with session config

* must use it

datafusion/common/src/config.rs

@@ -1365,8 +1365,7 @@ impl TableOptions {
     /// A new `TableOptions` instance with settings applied from the session config.
     pub fn default_from_session_config(config: &ConfigOptions) -> Self {
         let initial = TableOptions::default();
-        initial.combine_with_session_config(config);
-        initial
+        initial.combine_with_session_config(config)
     }
 
     /// Updates the current `TableOptions` with settings from a given session config.
@@ -1378,6 +1377,7 @@ impl TableOptions {
     /// # Returns
     ///
     /// A new `TableOptions` instance with updated settings from the session config.
+    #[must_use = "this method returns a new instance"]
     pub fn combine_with_session_config(&self, config: &ConfigOptions) -> Self {
         let mut clone = self.clone();
         clone.parquet.global = config.execution.parquet.clone();