Save cluster render shader from being optimized out entirely

servers/rendering/rendering_device.h

@@ -704,6 +704,8 @@ public:
 		SUPPORTS_MULTIVIEW,
 		SUPPORTS_FSR_HALF_FLOAT,
 		SUPPORTS_ATTACHMENT_VRS,
+		// If not supported, a fragment shader with only side effets (i.e., writes  to buffers, but doesn't output to attachments), may be optimized down to no-op by the GPU driver.
+		SUPPORTS_FRAGMENT_SHADER_WITH_ONLY_SIDE_EFFECTS,
 	};
 	virtual bool has_feature(const Features p_feature) const = 0;