ASP.NET Core 2.3 Razor Class Library is 404 Not Found

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Describe the bug

ASP.NET Core 2.1 Razor Class Library was displayed correctly. However, when I updated to ASP.NET Core 2.3, I got a 404 Not Found.

### Expected Behavior

I want to create a Razor Class Library in ASP.NET Core 2.3 as well as ASP.NET Core 2.1.

### Steps To Reproduce

see https://gitlab.com/masakura/aspnet-core-23-samples/-/tree/master/RazorClassLibrary

1. Creating a Web Application Project with Razor Class Library in ASP.NET Core 2.1
2. Run the project and verify that the Razor page of the RCL is displayed
3. Upgrade both projects to ASP.NET Core 2.3
4. 404 Not Found

### Exceptions (if any)

Downgrading the `Microsoft.AspNetCore.Mvc` package reference in the Razor Class Library to 2.1.3 works. As follows.

```xml




```

### .NET Version

.NET Framework 4.6.2 and .NET SDK 9

### Anything else?

_No response_