Fix the "attributes" key for testharness canvas element grid tests
No test currently uses custom context attributes in a canvas grid, so
this typo was left undetected.
Bug: 340005429
Change-Id: Ibab7f92cc43939e13700bbe5dc5846db98776ef0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5598921
Reviewed-by: Andres Ricardo Perez andresrperez@chromium.org
Commit-Queue: Jean-Philippe Gravel jpgravel@chromium.org
Cr-Commit-Position: refs/heads/main@{#1310850}