This change fixes the warning generated by clang when we enable -Wobjc-property-assign-on-object-type flag under the ARC environment.

Clang with the flag generates the warning if a property to an Objective-C object/block has an assign attribute because an assign property is treated as unretained property and it potentially becomes a dangling pointer.
The flag is added by llvm/llvm-project@52a503d4f333d
So using strong / weak / copy would be better in general.

selectedViewController is the currently selected view controller and the view must be in viewControllers which is strongly retained.
I think it's safe to use weak to selectedViewController.

PiperOrigin-RevId: 755861552

Author: Nobody

components/BottomNavigation/src/MDCBottomNavigationBarController.h

@@ -121,7 +121,7 @@ typedef NS_ENUM(NSInteger, MDCBottomNavigationBarLayoutMode) {
  The current selected view controller.  When setting this property, the view controller must be in
  @c viewControllers.
  */
-@property(nonatomic, assign, nullable) __kindof UIViewController *selectedViewController;
+@property(nonatomic, weak, nullable) __kindof UIViewController *selectedViewController;
 
 /**
  The index of the current selected tab item.  When setting this property the value must be in bounds