fix: dispose variable ShaderMaterials in GPUComputationRenderer.dispose() (#33318)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/jsm/misc/GPUComputationRenderer.js

@@ -339,6 +339,8 @@ class GPUComputationRenderer {
 
 				}
 
+				variable.material.dispose();
+
 			}
 
 		};