Mapping an object with getter only properties seems to be broken in v10.0.6 (works as expected in 7.4.0)

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Hello. I am trying to map an object with getter-only properties using a custom `Map` functon. This seems to be broken in v10.0.6, while it was fine in v7.4.0. See the following sample:
```c#
var typeAdapterConfig = new Mapster.TypeAdapterConfig();
typeAdapterConfig.Scan(typeof(Program).Assembly);
typeAdapterConfig.Compile();
var mapper = new MapsterMapper.Mapper(typeAdapterConfig);

var dto = new Dto { Data = new("new") };
Console.WriteLine(mapper.Map(dto, new Entity { Data = new("old") }).Data?.Value); // outputs "old" with v10.0.6, outputs "new" with v7.4.0
Console.WriteLine(mapper.Map(dto, new Entity()).Data?.Value); // outputs "new" with both v10.0.6 and v7.4.0
Console.WriteLine(mapper.Map(dto).Data?.Value); // outputs "new" with both v10.0.6 and v7.4.0

class Dto { public Data? Data { get; set; } }
class Entity { public Data? Data { get; set; } }
class Data(string value) { public string Value => value; }

class Mappings : Mapster.IRegister
{
public void Register(Mapster.TypeAdapterConfig config)
{
config.NewConfig()
.Map(x => x.Data, x => x.Data == null ? null : new Data(x.Data.Value));
}
}
```

Specifically this case seems to be broken:
```c#
var dto = new Dto { Data = new("new") };
var entity = mapper.Map(dto, new Entity { Data = new("old") });
```
I would expect the result entity's `Data` property to be mapped correctly from the source dto, as specified in the mapping function:
`config.NewConfig().Map(x => x.Data, x => x.Data == null ? null : new Data(x.Data.Value));`
As noted, Mapster v7.4.0 seems to be find, but v10.0.* seems to be broken.
Or maybe I am missing something here, please advise, thank you.

Start by running the supplied C# reproduction with Mapster v10.0.6 and compare the custom Dto-to-Entity mapping with v7.4.0. Trace the behavior of mapping onto an existing Entity when Data has a getter-only Value, and confirm done when the existing entity receives the new Data value while the other shown cases still pass.

Written by the indexing model from the issue text.