Test with wget-spider.sh on every build

[obscurerichard]

In #161 we introduced test/wget-spider.sh and we now run it vs. producton on every deploy (see #256) vs. the production site.

We should also be running this on every build. But to do that, we have to have a running site for every build. So this is blocked by not having a test site of some kind. freezingsaddles/freezing-compose#57 would resolve that by having GitHub Actions spin up an ephemeral test site for every build. So this would get unblocked when that is available.