no warning about unresolved references if they point to APIs that are filtered out

**DocFX Version Used**: 2.39.1.0

**Template used**: `default`

**Steps to Reproduce**:

1. Create a new csproj with theses classes:

```
namespace Classlibrary.Namespace1
{
public class PublicClass1 {}
public class PublicClass2 {}
public interface IPublicInterface1 {}
public interface IPublicInterface2 {}
}
namespace Classlibrary.Namespace2
{
public class PublicClass1 {}
public class PublicClass2 {}
public interface IPublicInterface1 {}
public interface IPublicInterface2 {}
}
```
2. init a new docfx projekt using `docfx init`

3. Add the following `apifilter.yml` to your project

```
apiRules:
- exclude:
uidRegex: ^ClassLibrary\.Namespace1$
type: Namespace
```

4. add the following in `index.md`
```
# xref short

The interface is not part of the api docs because it is filtered out.

# xref long

The interface [IPublicInterface1](xref:ClassLibrary.Namespace1.IPublicInterface1) is not part of the api docs because it is filtered out.
```

5. run
```
docfx metadata
docfx build
```

**Expected Behavior**:

When running `docfx build` I should get a warning about two unresolved cross references because when I look at actual docs using `docfx serve _site` I can see that the links are actually broken.

**Actual Behavior**:

No warnings are displayed at all.