headless: Use display buf for compare screenshot.

This is what the test actually uses too.

headless/StubHost.cpp

@@ -46,7 +46,7 @@ void HeadlessHost::SendDebugScreenshot(const u8 *pixbuf, u32 w, u32 h) {
 	const static u32 FRAME_HEIGHT = 272;
 
 	GPUDebugBuffer buffer;
-	gpuDebug->GetCurrentFramebuffer(buffer, GPU_DBG_FRAMEBUF_RENDER);
+	gpuDebug->GetCurrentFramebuffer(buffer, GPU_DBG_FRAMEBUF_DISPLAY);
 	const std::vector<u32> pixels = TranslateDebugBufferToCompare(&buffer, 512, 272);
 
 	ScreenshotComparer comparer(pixels, FRAME_STRIDE, FRAME_WIDTH, FRAME_HEIGHT);

test.py

@@ -150,6 +150,7 @@ tests_good = [
   "gpu/commands/cull",
   "gpu/commands/fog",
   "gpu/commands/material",
+  "gpu/complex/complex",
   "gpu/displaylist/alignment",
   "gpu/dither/dither",
   "gpu/filtering/mipmaplinear",
@@ -391,7 +392,6 @@ tests_next = [
   "font/shadowinfo",
   "gpu/clipping/guardband",
   "gpu/commands/light",
-  "gpu/complex/complex",
   "gpu/depth/precision",
   "gpu/displaylist/state",
   "gpu/filtering/linear",