Exercise GenerateAzureDevOpsBuildManifest MSBuild task in Arcade Validation

[missymessa]

The GenerateAzureDevOpsBuildManifest task was added to Publish.proj MSBuild project. We need to exercise this code path in Arcade Validation.

Related PRs

• Create modified msi package drop #5442
• Merge signing & asset manifests into a single manifest #5517
• Add build manifest #5210

Reference to code that needs testing

• https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.Arcade.Sdk/tools/Publish.proj
• https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.Arcade.Sdk/tools/SdkTasks/GenerateBuildManifest.proj
• https://github.com/dotnet/arcade/blob/master/src/Microsoft.DotNet.Arcade.Sdk/tools/Sign.props

[mmitche]

I removed this task in master (also in 5.0, PR is currently open). It's unused.