Increase the expiry time for sytem test artifacts

The test report is not that useful when system test artifacts expire in 1 week which means also that test history expires in 1 week. Here is a screenshot of the test history. It only shows up for the latest build, and even that is because I reran the latest build to renew artifacts, because they had expired before that.

Instability information is also not that useful with few builds.

I suggest increasing it from 1 week to 1 year. There is no hard limitation that I'm aware of that we want to respect regarding expiry dates. We just want to be sure that they get cleaned up eventually.