Due to a deliberate change in libcurl, the expiration is now capped to
at most 400 days.  We could solve this by choosing another date roughly
a year in the future, but would need to update the test next year.
This would be especially annoying for security branches.

Another option would be to actually parse the cookie list lines, but
that might not be worth the trouble.  Instead we just ignore the exact
timestamp created by libcurl.

[1] <curl/curl#15937>

Closes GH-17709.