[Codespaces] Debugging from VSCode hits an exception when running tests

```
{System.MissingMethodException: Constructor on type 'Microsoft.DotNet.XUnitExtensions.ConditionalClassDiscoverer' not found.
at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture) in /workspaces/runtime/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs:line 3866
at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes) in /workspaces/runtime/src/libraries/System.Private.CoreLib/src/System/Activator.RuntimeType.cs:line 39
at System.Activator.CreateInstance(Type type, Object[] args) in /workspaces/runtime/src/libraries/System.Private.CoreLib/src/System/Activator.cs:line 31
at Xunit.Sdk.ExtensibilityPointFactory.CreateInstance(IMessageSink diagnosticMessageSink, Type type, Object[] ctorArgs) in /_/src/xunit.execution/Sdk/ExtensibilityPointFactory.cs:line 25}
```

This is annoying, but apparently expected https://github.com/xunit/xunit/issues/556.
https://github.com/xunit/xunit/blob/474a71a57e842469fb05c970d5f64165eaea0b23/src/xunit.execution/Sdk/ExtensibilityPointFactory.cs#L22-L38