Hide UNSTABLE_isPending prop from docs (#4997)

Author: iamwillpowell

packages/@react-types/button/src/index.d.ts

@@ -74,7 +74,10 @@ export interface SpectrumButtonProps<T extends ElementType = 'button'> extends A
   style?: 'fill' | 'outline',
   /** The static color style to apply. Useful when the button appears over a color background. */
   staticColor?: 'white' | 'black',
-  /** Whether to disable events immediately and display a loading spinner after a 1 second delay. */
+  /** 
+   * Whether to disable events immediately and display a loading spinner after a 1 second delay. 
+   * @private
+   */
   UNSTABLE_isPending?: boolean,
   /**
    * Whether the button should be displayed with a quiet style.