[TEST] Enable image generation in marching cubes test

Switches the `image` parameter to `True` in the marching cubes test to ensure image generation is tested. This improves test coverage and better validates the functionality of the 3D plotting method.

Author: Leguark

test/test_modules/test_marching_cubes.py

@@ -52,6 +52,6 @@ def test_marching_cubes_implementation():
         gtv: gpv.GemPyToVista = gpv.plot_3d(
             model=model,
             show_data=True,
-            image=False,
+            image=True,
             show=True
         )