doc: update testing example code snippet for newest breaking changes

Testing.md

@@ -21,16 +21,17 @@ test "create container zon file" {
     }, .{});
     defer container.deinit();
 
-    const size: Size = .{
-        .rows = 20,
-        .cols = 30,
+    const size: Point = .{
+        .x = 30,
+        .y = 20,
     };
 
     const allocator = std.testing.allocator;
     var renderer: testing.Renderer = .init(allocator, size);
     defer renderer.deinit();
 
-    try container.handle(.{ .resize = size });
+    try renderer.resize(size);
+    container.resize(.{}, size);
     try renderer.render(Container(event.SystemEvent), &container);
 
     // NOTE: this is dependent on the working directory the test will be executed in