ASP0023 Ambiguous route warning false positive with Route attribute in abstract base controller

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the bug

There are a lot of issues regarding ASP0023 false positives: i found another strange dark corner case not yet reported.

I have a controller with two get actions with the same signature but the controller base class has the `Route` attribute with an action template match (i.e. `[Route("api/[controller]/[action]")]`). In this case the ASP0023 should not trigger.

But if the base controller class is also declared as `abstract` the ASP0023 rises up!!!

### Expected Behavior

_No response_

### Steps To Reproduce

```
using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();

var app = builder.Build();
app.MapControllers();
app.Run();

[Route("api/[controller]/[action]")]
[ApiController]
public abstract class MyControllerBase : ControllerBase //if you remove abstract ASP0023 disappears!!!!
{

}

public class MyController : MyControllerBase
{
[HttpGet("{a}")]
public IActionResult GetTest1(int a) => Ok(a);

[HttpGet("{a}")]
public IActionResult GetTest2(int a) => Ok(a * 2);
}

```

### Exceptions (if any)

_No response_

### .NET Version

8.0.400

### Anything else?

```
.NET SDK:
Version: 8.0.400
Commit: 36fe6dda56
Workload version: 8.0.400-manifests.56cd0383
MSBuild version: 17.11.3+0c8610977

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19043
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\8.0.400\

.NET workloads installed:
Configured to use loose manifests when installing new manifests.
[aspire]
Installation Source: VS 17.11.35222.181
Manifest Version: 8.1.0/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.aspire\8.1.0\WorkloadManifest.json
Install Type: FileBased

Host:
Version: 8.0.8
Architecture: x64
Commit: 08338fcaa5

.NET SDKs installed:
5.0.403 [C:\Program Files\dotnet\sdk]
6.0.404 [C:\Program Files\dotnet\sdk]
7.0.200 [C:\Program Files\dotnet\sdk]
8.0.400 [C:\Program Files\dotnet\sdk]
8.0.401 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.21 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.21 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.12 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
C:\Devel\ps\dev\global.json

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download
```