Code analysis warnings not treated as errors despite property

[AArnott]

Version Used:
dotnet SDK 5.0.100

Steps to Reproduce:

On a netstandard2.0 project, introduce a code analysis warning. Build with properties to treat warnings as errors.,

Minimal repro project: cabug.zip

Expected Behavior:

Build fails with error.
I expect just TreatWarningsAsErrors: true should be sufficient, but just to be sure I also set CodeAnalysisTreatWarningsAsErrors: true based on this documentation.

Actual Behavior:

Build succeeds after emitting a warning.

[mavasani]

Duplicate of #43051. Verified the issue is fixed if project file explicitly references a newer compiler toolset:

  <ItemGroup>
    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="3.9.0-2.final">
      <PrivateAssets>all</PrivateAssets>
      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
    </PackageReference>
  </ItemGroup>