[ToggleButtonGroup] Fixed incorrect A11y class name in child button added in single selection group.

PiperOrigin-RevId: 666950537

Author: pekingme

lib/java/com/google/android/material/button/MaterialButtonToggleGroup.java

@@ -387,13 +387,17 @@ public void setSingleSelection(boolean singleSelection) {
   }
 
   private void updateChildrenA11yClassName() {
+    String className = getChildrenA11yClassName();
     for (int i = 0; i < getChildCount(); i++) {
-      String className =
-          singleSelection ? RadioButton.class.getName() : ToggleButton.class.getName();
       getChildButton(i).setA11yClassName(className);
     }
   }
 
+  @NonNull
+  private String getChildrenA11yClassName() {
+    return singleSelection ? RadioButton.class.getName() : ToggleButton.class.getName();
+  }
+
   /**
    * Sets whether we prevent all child buttons from being deselected.
    *
@@ -517,6 +521,7 @@ private void setupButtonChild(@NonNull MaterialButton buttonChild) {
     buttonChild.setMaxLines(1);
     buttonChild.setEllipsize(TruncateAt.END);
     buttonChild.setCheckable(true);
+    buttonChild.setA11yClassName(getChildrenA11yClassName());
 
     // Enables surface layer drawing for semi-opaque strokes
     buttonChild.setShouldDrawSurfaceColorStroke(true);