MediaVulkanGpuTest: use AIMAGE_FORMAT_PRIVATE.

In the use case ImageReader does not need to enforce the color
format, therefore use PRIVATE (opaque) format.

Bug: 380386975
Test: atest android.graphics.cts.MediaVulkanGpuTest
(cherry picked from https://android-review.googlesource.com/q/commit:bc727d3d0c56c1cf54154de10f9d9f5a1a1207d2)
Merged-In: I7bbfd4a5bfa107cce1e2770f26d0e742094fa4ab
Change-Id: I7bbfd4a5bfa107cce1e2770f26d0e742094fa4ab

tests/tests/graphics/jni/android_graphics_cts_MediaVulkanGpuTest.cpp

diff --git a/tests/tests/graphics/jni/android_graphics_cts_MediaVulkanGpuTest.cpp b/tests/tests/graphics/jni/android_graphics_cts_MediaVulkanGpuTest.cpp
index fd570a8..d5dd3af 100644
--- a/tests/tests/graphics/jni/android_graphics_cts_MediaVulkanGpuTest.cpp
+++ b/tests/tests/graphics/jni/android_graphics_cts_MediaVulkanGpuTest.cpp
@@ -28,7 +28,7 @@
 
 static constexpr uint32_t kTestImageWidth = 1920;
 static constexpr uint32_t kTestImageHeight = 1080;
-static constexpr uint32_t kTestImageFormat = AIMAGE_FORMAT_YUV_420_888;
+static constexpr uint32_t kTestImageFormat = AIMAGE_FORMAT_PRIVATE;
 static constexpr uint64_t kTestImageUsage =
     AHARDWAREBUFFER_USAGE_GPU_SAMPLED_IMAGE;
 static constexpr uint32_t kTestImageCount = 3;