* Add unit test for injected 404 routes
* Add fixture test for injected 404 routes
* Use any route pattern to find custom 404
* Fix frozen lockfile error
* Use `route` instead of `pattern` to match custom 404
Dynamic catch-all routes can match against `/404/` but will then error because they’re not actually designed to handle a param of `'404'`. Testing `route` instead excludes dynamic routes (because they’ll contain dynamic segments inside square brackets). Not sure if someone might _want_ to render the 404 via a dynamic route, but we already don’t support that, so this doesn’t change anything.
* Fix injected 404 fixture
* Add tests for `src/pages/404.html`
* Add changeset
* Fix lockfile
* And again
