Update DNS Shotgun parameters for an updated dataset

Update DNS Shotgun parameters for an updated dataset

We've switched to an updated dataset for shotgun jobs. The change in
underlying traffic caused the more sensitive doh-get (and partially dot)
jobs to overload the resolver, making the jobs unstable and unreliable,
due to an increased number of timeouts.

Readjust the load parameters slightly to avoid exceeding ~2 % of
timeouts in the cold cache scenario to stabilize the job results.