`dotnetup dotnet` swallows `--help` argument instead of passing it to `dotnet`

### Prerequisites

- [x] I have read the [dotnetup documentation](https://github.com/dotnet/sdk/tree/release/dnup/documentation/general/dotnetup).
- [x] I have searched for [existing dotnetup issues](https://github.com/dotnet/sdk/issues?q=is%3Aissue%20state%3Aopen%20label%3Adotnetup).
- [x] I have searched for [existing dotnetup discussions](https://github.com/dotnet/sdk/discussions/categories/dotnetup).

### Issue type

Bug report

### Description

I will use `dotnet run` as an example command but I think this applies to any `dotnet` CLI command.

When I run `dotnetup dotnet run --help`, I expect to see the same output as `dotnet run --help`:

```
Description:
.NET Run Command

Usage:
dotnet run [...] [options]

Arguments:
Arguments passed to the application that is being run. []

Options:
-c, --configuration The configuration to run for. The default for most projects is 'Debug'.
-f, --framework The target framework to run for. The target ...

```

Instead, I see the help output for `dotnetup dotnet`:

```
Description:
Run a command using the dotnetup-managed dotnet installation.

Usage:
dotnetup dotnet [options] [[--] ...]]

Options:
-?, -h, --help Show help and usage information

Additional Arguments:
Arguments passed to the application that is being run.
```

### dotnetup version

_No response_