Improve error message when deserializing perf-config.json in the site

Author: Kobzol

site/src/benchmark_metadata/mod.rs

@@ -52,7 +52,12 @@ fn load_compile_benchmark_metadata() -> HashMap<String, CompileBenchmarkMetadata
                 release_metadata,
             } = metadata;
             let perf_config: BenchmarkConfig =
-                serde_json::from_value(perf_config).expect("Cannot deserialize perf-config.json");
+                serde_json::from_value(perf_config).unwrap_or_else(|error| {
+                    panic!(
+                        "Cannot deserialize perf-config.json for benchmark {name}: {:?}",
+                        error
+                    );
+                });
 
             let metadata = CompileBenchmarkMetadata {
                 perf_config,