Use pattern matching instead of casting

See https://openjdk.org/jeps/305

modules/core/src/main/java/org/shakespeareframework/RetryableQuestion.java

@@ -46,16 +46,16 @@ default boolean isIgnoredException(Exception exception) {
    * @return {@code true} if the given answer is acceptable
    */
   default boolean acceptable(A answer) {
-    if (answer instanceof Optional<?>) {
-      return ((Optional<?>) answer).isPresent();
-    } else if (answer instanceof Collection<?>) {
-      return !((Collection<?>) answer).isEmpty();
-    } else if (answer instanceof Map<?, ?>) {
-      return !((Map<?, ?>) answer).isEmpty();
-    } else if (answer instanceof Object[]) {
-      return ((Object[]) answer).length > 0;
-    } else if (answer instanceof Boolean) {
-      return (Boolean) answer;
+    if (answer instanceof Optional<?> optionalAnswer) {
+      return optionalAnswer.isPresent();
+    } else if (answer instanceof Collection<?> collectionAnswer) {
+      return !collectionAnswer.isEmpty();
+    } else if (answer instanceof Map<?, ?> mapAnswer) {
+      return !mapAnswer.isEmpty();
+    } else if (answer instanceof Object[] arrayAnswer) {
+      return arrayAnswer.length > 0;
+    } else if (answer instanceof Boolean booleanAnswer) {
+      return booleanAnswer;
     }
     return answer != null;
   }