website: Update mailing list links.

We've moved our mailing list server. As such the links need updated.

Change-Id: I435940321ab41e183d8666ace8c7fd1443fd86d6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/59169
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>
1 file changed