[gm3][ntp] Update webstore toast strings

Bug: 1470415
Change-Id: I411866c1bbf3139e071d6e5dbfc724cbc1809147
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4754502


Reviewed-by: Riley Tatum <rtatum@google.com>
Commit-Queue: Roman Arora <romanarora@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1180437}