validation: compute shader must include 'workgroup_size' in its attributes

Bug: tint:884
Change-Id: If96c6df3247fee142a779117fa26d006afd4f7ef
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/55680
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/test/ptr_ref/load/local/ptr_function.wgsl.expected.wgsl b/test/ptr_ref/load/local/ptr_function.wgsl.expected.wgsl
index be1837a..4bd46dd 100644
--- a/test/ptr_ref/load/local/ptr_function.wgsl.expected.wgsl
+++ b/test/ptr_ref/load/local/ptr_function.wgsl.expected.wgsl
@@ -1,4 +1,4 @@
-[[stage(compute)]]
+[[stage(compute), workgroup_size(1)]]
 fn main() {
   var i : i32 = 123;
   let p : ptr<function, i32> = &(i);