go.dev: decrease HaTS sample size
go.dev: decrease HaTS sample size

We're getting more responses than we need for go.dev HaTS.
Decreasing the sample size from 40% to 10%.

Change-Id: I9aae64db6a675da27823ad6f4b006f6dd44ce1bf
Reviewed-on: https://go-review.googlesource.com/c/website/+/362954
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website