Only add strikes when explicitly declining AutofillAI prompts.

Prior to this CL ignoring a prompt would also add strikes. This CL
fixes that.

Bug: 399062284
Change-Id: I9a9d56c1f917a1ded33b626c70bd92b02be3f77e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6322148
Auto-Submit: Jan Keitel <jkeitel@google.com>
Reviewed-by: Christoph Schwering <schwering@google.com>
Commit-Queue: Christoph Schwering <schwering@google.com>
Cr-Commit-Position: refs/heads/main@{#1428019}