Add skip for Pokemon Masters Ex validation warning

This warning was generated in the Pokemon Masters Ex trace due to
application issues and does not cause the test to fail but does create
confusing output: Undefined-Value-ShaderFragmentOutputMismatch.
Added it to kSkippedMessages.

Test: angle_trace_tests --gtest_fitler=*pokemon_masters_ex
Bug: b/319228278
Change-Id: I57bd9cca4b9bb5b681fb26884c9ba6ce8e66c667
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5334761
Commit-Queue: Mark Łobodziński <[email protected]>
Reviewed-by: Cody Northrop <[email protected]>

src/libANGLE/renderer/vulkan/RendererVk.cpp

@@ -280,6 +280,7 @@ constexpr const char *kSkippedMessages[] = {
     // https://issuetracker.google.com/319228278
     "VUID-vkCmdDrawIndexed-format-07753",
     "VUID-vkCmdDraw-format-07753",
+    "Undefined-Value-ShaderFragmentOutputMismatch",
 };
 
 // Validation messages that should be ignored only when VK_EXT_primitive_topology_list_restart is