[Compare] Update context menu entry point string

"Show specifications" to "Compare tabs"

Bug: 362352843
Change-Id: I83c3d27746505be0ea85dfe699d668c7d92c33db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5815467


Reviewed-by: Yue Zhang <yuezhanggg@chromium.org>
Auto-Submit: Matthew Jones <mdjones@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1348763}