[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}

infra/config/global/cr-buildbucket.cfg

@@ -2836,6 +2836,9 @@ buckets {
       dimensions: "cores:8"
       dimensions: "cpu:x86-64"
       service_account: "chromium-try-builder@chops-service-accounts.iam.gserviceaccount.com"
+      # Max. pending time for builds. CQ considers builds pending >2h as timed
+      # out: http://shortn/_8PaHsdYmlq. Keep this in sync.
+      expiration_secs: 7200 # 2h
       execution_timeout_secs: 10800  # 3h
       swarming_tags: "vpython:native-python-wrapper"
       build_numbers: YES