Add trailing underscore to the backing field matching convention

See https://github.com/dotnet/efcore/issues/23703

So this is not needed:

```C#
modelBuilder.Entity<Post>().Navigation(e => e.TagsInPostsData).HasField("tagsInPostsData_");
modelBuilder.Entity<Tag>().Navigation(e => e.PostsInTagsData).HasField("postsInTagsData_")
```
