Fix build errors: remove duplicate braces, add missing using

Author: fdcastel

src/FirebirdSql.Data.FirebirdClient.Benchmarks/BenchmarkConfig.cs

@@ -20,6 +20,7 @@
 using BenchmarkDotNet.Exporters;
 using BenchmarkDotNet.Jobs;
 using BenchmarkDotNet.Order;
+using BenchmarkDotNet.Toolchains;
 using BenchmarkDotNet.Toolchains.CsProj;
 using BenchmarkDotNet.Toolchains.DotNetCli;
 using BenchmarkDotNet.Validators;

src/FirebirdSql.Data.FirebirdClient.Benchmarks/CommandBenchmark.Fetch.cs

@@ -89,6 +89,4 @@ public async Task<object> FetchAsync()
 		}
 		return last;
 	}
-}
-	}
 }