[CardView] Fix potential Proguard/Dexguard/R8(?) optimization problem

Resolves #790

GIT_ORIGIN_REV_ID=fddc631d7a7c010044ab66247bec85f0aba097aa
PiperOrigin-RevId: 282769919

(cherry picked from commit db7fde2)

Author: rossbacher

lib/java/com/google/android/material/card/MaterialCardView.java

@@ -100,7 +100,7 @@ public interface OnCheckedChangeListener {
    * Keep track of when {@link CardView} is done initializing because we don't want to use the
    * {@link Drawable} that it passes to {@link #setBackground(Drawable)}.
    */
-  private final boolean isParentCardViewDoneInitializing;
+  private boolean isParentCardViewDoneInitializing;
 
   private boolean checked = false;
   private boolean dragged = false;