test: properly used isA matcher

packages/pinball_flame/test/src/shapes/arc_shape_test.dart

@@ -13,7 +13,7 @@ void main() {
           arcRadius: 10,
           angle: 2 * math.pi,
         ),
-        isA<ArcShape>,
+        isA<ArcShape>(),
       );
     });
   });

packages/pinball_flame/test/src/shapes/bezier_curve_shape_test.dart

@@ -15,7 +15,7 @@ void main() {
             Vector2(10, 10),
           ],
         ),
-        isA<BezierCurveShape>,
+        isA<BezierCurveShape>(),
       );
     });
   });

packages/pinball_flame/test/src/shapes/ellipse_shape_test.dart

@@ -13,7 +13,7 @@ void main() {
           majorRadius: 10,
           minorRadius: 8,
         ),
-        isNotNull,
+        isA<EllipseShape>(),
       );
     });