In a Lobsters thread about hosting Zig mirrors, @kristoff-it linked to this guide, and I thought it belonged here, as it's a great resource for community members interested in hosting a mirror.

It probably makes sense for this to be a full release rather than a
patch release where possible. The actual motivation here is that
mlugg/setup-zig currently uses this version exactly. In fact, for `-dev`
versions, I don't think it even *can* do anything else, since there may
be breaking changes between `0.A.0-dev+...` and `0.A.0`.

* `build.zig.zon`: bump `minimum_zig_version` to full release
* `check-mirrors`: dump error trace if `fetch` returns error