pytests/test_regulators: use correct regulator for GPU

pytests/test_regulators.py

@@ -13,4 +13,4 @@ def check_voltage(regulator, voltage):
 
 # This is true until the GPU does DVFS
 def test_gpu_regulator():
-    check_voltage("buck5", 900)
+    check_voltage("buck3", 900)