[Compare] Fix disclosure dialog width

Bug: 362290369
Change-Id: I009daebdc6855f8b57da78770228d7e16d1fcb3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5815396


Reviewed-by: Paul Adedeji <pauladedeji@google.com>
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1348029}