rust: increase release artifact download parallelism

This appears to help a little on my 1 gbps Internet.

Author: indygreg

src/github.rs

@@ -206,7 +206,7 @@ pub async fn command_fetch_release_distributions(args: &ArgMatches) -> Result<()
         }
     }
 
-    let mut buffered = futures::stream::iter(fs).buffer_unordered(8);
+    let mut buffered = futures::stream::iter(fs).buffer_unordered(24);
 
     let mut install_paths = vec![];