[cr-buildbucket] Set 2h pending timeout for luci.chromium.try builds

This is to synchronize it with the CQ settings which cosinders builds pending
>2h as timed out.

Bug: 908943
Change-Id: I56285d4236eeae1a38e525ea0f18c68f80c07d14
Reviewed-on: https://chromium-review.googlesource.com/c/1352446
Commit-Queue: Sergey Berezin <sergeyberezin@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611296}