Fix T68413: gpu module example in docs produces unexpected results

doc/python_api/examples/gpu.5.py

@@ -4,6 +4,7 @@ Mesh with Random Vertex Colors
 """
 import bpy
 import gpu
+import bgl
 import numpy as np
 from random import random
 from gpu_extras.batch import batch_for_shader
@@ -30,7 +31,9 @@ batch = batch_for_shader(
 
 
 def draw():
+    bgl.glEnable(bgl.GL_DEPTH_TEST)
     batch.draw(shader)
+    bgl.glDisable(bgl.GL_DEPTH_TEST)
 
 
 bpy.types.SpaceView3D.draw_handler_add(draw, (), 'WINDOW', 'POST_VIEW')