[Bug]: Specifying -graphBuild twice causes misleading error MSB1057

### Issue Description

For ordinary MSBuild command-line arguments, redundant arguments are accepted (for instance, setting defaults in Directory.Build.rsp and overriding them at the command line). But if `-graphBuild` is specified more than once, an error occurs.

### Steps to Reproduce

`dotnet msbuild -t:Build -graphBuild:True -graphBuild:True MyProj.csproj`

### Expected Behavior

Argument override is accepted.

### Actual Behavior

```
MSBuild version 17.10.4+10fbfbf2e for .NET
MSBUILD : error MSB1057: Graph build value is not valid.
Switch: True
```

### Analysis

_No response_

### Versions & Configurations

dotnet: 8.0.304
MSBuild: 17.10.4.21802