Add more shards for chrome android and weblayer wpt builders

After enabled reftests, we see the two builders timed out constantly.
Give them more shards to solve the issue.

Do not run webdriver tests on WPT Android builders. Webdriver tests
are running through a different test suite. So no need to run it here.

Bug: 1235650
Change-Id: I41d439870572027ad656ce523055cd4b77750e5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3419264
Reviewed-by: Rakib Hasan <rmhasan@google.com>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Weizhong Xia <weizhong@google.com>
Cr-Commit-Position: refs/heads/main@{#965782}