Increased samples for VolumeLightBunnyRadianceGrayRectConfig case due…

… to failing test.

src/integrators/tests/test_ad_integrators.py

@@ -514,7 +514,7 @@ def __init__(self) -> None:
             'type': 'ply',
             'filename': 'resources/data/common/meshes/bunny_watertight.ply',
         })
-        self.spp = 1024
+        self.spp = 2048
         self.error_mean_threshold = 0.1
 
 # Intensity of a spherical volume emitter illuminating a gray rectangle from offscreen