docs(material/bottom-sheet): update panelClass comment (#33321)

Updates the comment for the bottom sheet to mention the correct element.

Fixes #33103.

Author: crisbeto

src/material/bottom-sheet/bottom-sheet-config.ts

@@ -30,7 +30,7 @@ export class MatBottomSheetConfig<D = any> {
    */
   injector?: Injector;
 
-  /** Extra CSS classes to be added to the bottom sheet container. */
+  /** Extra CSS classes to be added to the overlay panel containing the bottom sheet. */
   panelClass?: string | string[];
 
   /** Text layout direction for the bottom sheet. */