[macos] Shipping dotnet-* tools unsigned

### Description

The released global diagnostic tools are not signed.

For instance
```
codesign -v $(which dotnet-sos)

% codesign -v $(which dotnet-sos)
/Users/stmaclea/.dotnet/tools/dotnet-sos: code object is not signed at all
In architecture: arm64
```

This is problematic for Apple Silicon because it runs on Big Sur and the kernel will automatically kill all unsigned binaries.

```
zsh: killed /Users/stmaclea/.dotnet/tools/dotnet-sos
```

It is not clear whether this affects all Big-Sur architectures.

/cc @hoyosjs @mikem8361 @vitek-karas