Fix erroneous stash access in Attribution Reporting WPT server
The stash is a property of the server attribute, not the request.
Bug: 357924626
Change-Id: I57e8a6cc46a140218f410eb946894431f30d6aba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5770491
Reviewed-by: Weizhong Xia weizhong@google.com
Auto-Submit: Andrew Paseltiner apaseltiner@chromium.org
Commit-Queue: Weizhong Xia weizhong@google.com
Commit-Queue: Andrew Paseltiner apaseltiner@chromium.org
Cr-Commit-Position: refs/heads/main@{#1338581}