removed the plain variant condition

Author: Mash707

packages/react-core/src/components/Button/Button.tsx

@@ -222,8 +222,8 @@ const ButtonBase: React.FunctionComponent<ButtonProps> = ({
         isAriaDisabled && styles.modifiers.ariaDisabled,
         isClicked && styles.modifiers.clicked,
         isInline && variant === ButtonVariant.link && styles.modifiers.inline,
-        isFavorite && variant === ButtonVariant.plain && styles.modifiers.favorite,
-        isFavorite && isFavorited && variant === ButtonVariant.plain && styles.modifiers.favorited,
+        isFavorite && styles.modifiers.favorite,
+        isFavorite && isFavorited && styles.modifiers.favorited,
         isDanger && (variant === ButtonVariant.secondary || variant === ButtonVariant.link) && styles.modifiers.danger,
         isLoading !== null && variant !== ButtonVariant.plain && styles.modifiers.progress,
         isLoading && styles.modifiers.inProgress,