[ntp] Split NewTabPageAppTest.All into multiple runs

The single NewTabPageAppTest.All timed out on some bots. Splitting the
suite into multiple runs should alleviate the timeout pressure.

Fixed: 1217097
Change-Id: I67273a1c3c6c2ac9c8884d84c2468b9913b08133
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3233179
Auto-Submit: Tibor Goldschwendt <[email protected]>
Commit-Queue: Moe Ahmadi <[email protected]>
Reviewed-by: Moe Ahmadi <[email protected]>
Cr-Commit-Position: refs/heads/main@{#933513}