Can't add Testing package via `aspire add`

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Describe the bug

I tried to add the `Aspire.Hosting.Testing` package to a test project via `aspire add Testing`. I was expecting it to find the testing package, however `aspire add` failed to find the package

### Expected Behavior

The package search should find the testing package, and let me add it.

### Steps To Reproduce

_No response_

### Exceptions (if any)

_No response_

### .NET Version info

_No response_

### Anything else?

_No response_