fix Rust 1.86.0 clippy (#273)

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/solc-json-interface/src/standard_json/output/source.rs

@@ -196,7 +196,7 @@ impl Source {
                     _ => None,
                 },
             )
-            .last()
+            .next_back()
             .ok_or_else(|| anyhow::anyhow!("The last contract not found in the AST"))
     }
 }