Fix "My Jobs" tab in user dashboard

Nowadays `Builds` doesn't reference `Project` directly anymore. This
means that simply resolving both `jobset` and `project` with a single
JOIN from `Builds` doesn't work anymore. Instead we need to resolve the
relation to `jobset` first and then the relation to `project`.

For similar fixes see e.g. c7c4759600.

t/jobs/basic.nix

@@ -4,6 +4,8 @@ with import ./config.nix;
     mkDerivation {
       name = "empty-dir";
       builder = ./empty-dir-builder.sh;
+      meta.maintainers = [ "alice@invalid.org" ];
+      meta.outPath = "${placeholder "out"}";
     };
 
   fails =