Slightly increase D3D12 leak check threshold

* We're now caching descriptor data so we deliberately allocate a bit more
  memory. This will still allow us to catch egregious leaks.

util/test/tests/D3D12/D3D12_Leak_Check.py

@@ -11,7 +11,7 @@ class D3D12_Leak_Check(rdtest.TestCase):
     def check_capture(self):
         memory: int = rd.GetCurrentProcessMemoryUsage()
 
-        if memory > 500*1000*1000:
+        if memory > 600*1000*1000:
             raise rdtest.TestFailureException("Memory usage of {} is too high".format(memory))
 
         rdtest.log.success("Capture {} opened with reasonable memory ({})".format(self.demos_frame_cap, memory))