Some web servers in our htpdate pool return incorrect time

I've seen test suite failures caused by htpdate setting the time 6-10 minutes in the past, while our test suite expects the clock to be less than 5 minutes incorrect.

So I tested the 2 servers that were involved in that test:

• https://leap.se's Date header is currently 6 minutes in the past
• https://en.wikipedia.org's date header is currently 10 minutes in the past