PostgreSQL 无法使用json的text保存数据

类

```
[Table(Name = "Work2")]
public class Work
{
[Column(IsIdentity = true, IsPrimary = true)]
public long Id { get; set; }

[JsonMap]
[Column(DbType = "text",MapType =typeof(string))]
public Dictionary Test6 { get; set; }
}
```

插入
```
var aaa = Enumerable.Range(1, 1).Select(o => new Work()
{
Id = 1,
Test6 = new Dictionary { { "key1", "value1" }, { "key2", "value2" } }
}).ToList();

db.Insert(aaa).ExecuteAffrows();
```

数据库
"Id" "Test6"
1 "System.Collections.Generic.Dictionary`2[System.String,System.String]"

Use the supplied Work model and db.Insert reproduction as the starting point; inspect the PostgreSQL mapping path for [JsonMap] with Column DbType="text" and MapType=typeof(string). Confirm completion by rerunning the insert and verifying that Test6 stores JSON text rather than the Dictionary type name.

Written by the indexing model from the issue text.