[Bug] Failure with inheritdoc under certiain circumstances

**Actual behavior**
docfx fails to inherit documentation when is used under certain circumstances:
- inheriting from .net type (e.g. object.ToString(), object.Equals(), etc) and
- project TargetFramework is "netstandard2.0"


Please note that doc inheritance **works well**:
- for other TargetFramework, e.g. "net6.0"
- for types created within the project, e.g.
- with Visual Studio hint


**Expected behavior**
Documentation should be inherited like it happens for other target frameworks or for other types.

**To Reproduce**
See minimal sample project here:
https://github.com/Lesnik4u/DocFxInheritdocIssueTest
particularly, see the override MyLibBaseClass.ToString().

```C#
namespace MyClassLibrary
{
/// Description in the BASE class. (TargetFramework = netstandard2.0)
public class MyLibBaseClass
{
/// Description in the BASE class.
public virtual void MyMethod() { }

// inheritdoc FAILURE!
///
public override string ToString() => "";
}

///
public class MyLibChildClass : MyLibBaseClass
{
///
public override void MyMethod() { }
}
}
```

**Context:**
- OS: Windows 10 pro
- Docfx version: v2.73.1
- .NET Core SDK: v6.0.300