Explain why tests/autodiff/diff-ptr-type-array.slang is disabled for WGPU (#5702)

This closes #5613.

Co-authored-by: Ellie Hermaszewska <[email protected]>

Author: aleino-nv

tests/autodiff/diff-ptr-type-array.slang

@@ -1,6 +1,6 @@
 //TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -shaderobj -output-using-type
 //TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -vk -shaderobj -output-using-type
-// WGSL: Runtime-sized arrays not in 'storage' address space are being generated #5613
+// Not supported in WGSL: Arrays of textures or buffers
 //DISABLE_TEST(compute):COMPARE_COMPUTE:-wgpu
 
 //TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer