Fix Cypher query to use agtype casting for bignumber parameter

Author: nikoraes

test/Npgsql.AgeTests/AgeIntegrationTests.cs

@@ -215,7 +215,7 @@ public async Task ExecuteCypherQueryAsync_WithStringToAgtypeMap_Should_Work()
 
         await using var command = connection.CreateCypherCommand(
             graphName,
-            "WITH '{\"bignumber\":5e24}' as obj RETURN obj.bignumber"
+            "WITH '{\"bignumber\":5e24}'::agtype as obj RETURN obj.bignumber"
         );
         await using var dataReader = await command.ExecuteReaderAsync();