cv: bump threshold before warning about too early task execution.
cv: bump threshold before warning about too early task execution.

R=qyearsley, yiwzhang

Bug: 1156241
Change-Id: I711d737ca6ee3839e4b8526f2e378bd3820901cc
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2596256
Auto-Submit: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@google.com>
Commit-Queue: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>
Reviewed-by: Yiwei Zhang <50b2a565e2e78c292794832469a30ce5abc9959c@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go