scraper: ignore clippy warning

It wants us to break up this declaration but let's just ignore it for now.

```
error: very complex type used. Consider factoring parts into `type` definitions
   --> fcos-graph-builder/src/scraper.rs:105:10
    |
105 |       ) -> impl Future<
    |  __________^
106 | |         Output = Result<(HashMap<String, graph::Graph>, HashMap<String, graph::Graph>), Error>,
107 | |     > {
    | |_____^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#type_complexity
    = note: `-D clippy::type-complexity` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::type_complexity)]`
```

Author: dustymabe

fcos-graph-builder/src/scraper.rs

@@ -100,6 +100,7 @@ impl Scraper {
     }
 
     /// Combine release-index and updates metadata.
+    #[allow(clippy::type_complexity)]
     fn assemble_graphs(
         &self,
     ) -> impl Future<