[Bug] Markdown Metadata Output For Generic Classes Doesn't Show Derived Section

Describe the bug Not sure why, but the markdown metadata output format doesn't seem to include a Derived section on pages that happen to be generic, even though they would be listed in the yaml counterpart.

To Reproduce Steps to reproduce the behavior:

Create a dummy project with a generic base class and one or more derived classes, e.g.:
```
namespace DocFXTest;
public class GenericBaseClass<T>
{
}
```

public class GenericDerivedClass : GenericBaseClass { }

2. Run DocFX with a minimal config for the project, i.e.:

{ "metadata": [ { "src": [ ... ], "dest": ... } ] }

4. Observe that the `derivedClasses` section is present in `DocFXTest.GenericBaseClass-1.yml:`

... derivedClasses:

DocFxTest.GenericDerivedClass`1 ...

5. Modify the config to make the outputFormat markdown:

{ "metadata": [ { ... "outputFormat": "markdown" } ] }

6. Run DocFX again.
**Expected behavior**
One of the resulting files, `DocFXTest.GenericBaseClass-1.md`, should have a `Derived` section, i.e.:

...

Derived

GenericDerivedClass<T> ...

Actual behavior DocFXTest.GenericBaseClass-1.md, does not have a Derived section, i.e.:

# <a id="DocFxTest_GenericBaseClass_1"></a> Class GenericBaseClass<T\>

Namespace: [DocFxTest](DocFxTest.md)  
Assembly: DocFxTest.dll

```csharp
public class GenericBaseClass<T>

Type Parameters

T

Inheritance

object ← GenericBaseClass<T>

Inherited Members

object.Equals(object?), object.Equals(object?, object?), object.GetHashCode(), object.GetType(), object.MemberwiseClone(), object.ReferenceEquals(object?, object?), object.ToString()



**Context (please complete the following information):**
- Docfx version: 2.77.0
- Template: markdown (api output format)

**Additional context**
The trigger condition appears to be the base class that is generic, and only that page is affected. Non-generic base classes will include a `#### Derived` section.

dotnet / docfx