MSBuildWorkspace reports warnings as errors/failures

[svick]

Version Used: Roslyn 4.11.0

Steps to Reproduce:

Run this code:

using Microsoft.CodeAnalysis.MSBuild;

var workspace = MSBuildWorkspace.Create();

var project = await workspace.OpenProjectAsync(@"..\..\..\..\project\project.csproj");

foreach (var diagnostic in workspace.Diagnostics)
{
    Console.WriteLine($"{diagnostic.Kind}: {diagnostic.Message}");
}

Where project.csproj is:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
  </ItemGroup>

</Project>

Expected Behavior:

The workspace reports the NU1903 warning about a vulnerability as a warning, i.e. the output should be:

Warning: Msbuild failed when processing the file 'C:\src\tmp\roslynworkspaceapp\project\project.csproj' with message: Package 'Newtonsoft.Json' 12.0.3 has a known high severity vulnerability, https://github.com/advisories/GHSA-5crp-9r3c-p9vr

Actual Behavior:

The warning is reported as a failure:

Failure: Msbuild failed when processing the file 'C:\src\tmp\roslynworkspaceapp\project\project.csproj' with message: Package 'Newtonsoft.Json' 12.0.3 has a known high severity vulnerability, https://github.com/advisories/GHSA-5crp-9r3c-p9vr

The problem is in Microsoft.CodeAnalysis.MSBuild.DiagnosticReporter, whose Report(DiagnosticLog log) method ignores DiagnosticLogItem.Kind.

[tmat]

Related: #75170