Shaders: fix an accidental copypaste error in MeshVisualizer test.

Causes an error on WebGL, because the ObjectId attribute isn't bound.
The 2D variant doesn't use it and passes, so this was a clear mistake.

src/Magnum/Shaders/Test/MeshVisualizerGLTest.cpp

@@ -3280,7 +3280,7 @@ template<MeshVisualizerGL3D::Flag flag> void MeshVisualizerGLTest::renderDefault
     GL::Mesh icosphere = MeshTools::compile(Primitives::icosphereSolid(0));
 
     MeshVisualizerGL3D shader{MeshVisualizerGL3D::Configuration{}
-        .setFlags(MeshVisualizerGL3D::Flag::InstancedObjectId|flag)};
+        .setFlags(MeshVisualizerGL3D::Flag::ObjectId|flag)};
     shader.bindColorMapTexture(_colorMapTexture);
 
     if(flag == MeshVisualizerGL3D::Flag{}) {