`dotnet tool restore` message is insufficiently helpful

### Describe the bug

Running `dotnet tool restore` on a project yielded this message:

### To Reproduce

The problem is that one of the tools referenced in `.config/dotnet-tools.json` is not supported outside of Windows, so running `dotnet tool restore` caused this problem. (The package may be malformed for this scenario; I didn't investigate further.) The message from `dotnet tool restore` is not only mostly unactionable, it's especially unactionable because we have no idea what package is to blame.

To reproduce:

1. Create a `.config/dotnet-tools.json` file with the following contents:

```json
{
"version": 1,
"isRoot": true,
"tools": {
"sign": {
"version": "0.9.1-beta.26127.1",
"commands": [
"sign"
],
"rollForward": false
}
}
}
```

2. Run `dotnet tool restore` on a non-Windows OS (like Linux or macOS)

Note that the message here is less useful than me trying to prove which package was the issue:

At a bare minimum, I would expect `dotnet tool restore` to give a similar message that includes the package name. (I don't know why the message here starts with "failed to update", since the `sign` tool is not currently installed globally. That would be a different bug. 😄)