[swarming] fix regex for task id
[swarming] fix regex for task id

task id is hexadecimal.

Change-Id: Id978b0b3df68f23399c5e4b8c885766c8af2f653
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2574036
Commit-Queue: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

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