SignCheckTask Returns False Without Logging an Error

- [ ] This issue is blocking
- [x] This issue is causing unreasonable pain

### Context
MSBuild is upgrading to Arcade 5.0 and we're [hitting errors](https://dev.azure.com/devdiv/DevDiv/_build/results?buildId=4323092&view=results) in our pipeline builds that our `nupkg` files aren't signed properly.
### The Problem
These errors aren't helpful, as all we see is: `c:\src\git\msbuild\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20510.1\tools\SdkTasks\SigningValidation.proj(48,5): error MSB4181: The "SignCheckTask" task returned false but did not log an error. [c:\src\git\msbuild\.packages\microsoft.dotnet.arcade.sdk\5.0.0-beta.20510.1\tools\SdkTasks\SigningValidation.proj]`
### Some sort of solution
If the task _would_ fail, throw an error that provides context as to why it failed.
### Why it's blocking
I'm not sure how to move forward migrating to arcade 5.0 because I'm not sure what's going wrong.

### Extra Info
Contents of `signcheck.errors.log`
`Signing issues found`
Contents of `signcheck.log`
```
Starting execution of SignCheck.

Results

[File] Microsoft.Build.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Conversion.Core.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Engine.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Framework.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Localization.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Runtime.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Tasks.Core.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Utilities.Core.16.9.0-preview-20622-01.nupkg, Signed: False
[File] MsBuild.Engine.Corext.16.9.0-preview-20622-01.nupkg, Signed: False
[File] VS.ExternalAPIs.MSBuild.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Localization.16.9.0-preview-20622-01.nupkg, Signed: False
[File] MsBuild.Engine.Corext.16.9.0-preview-20622-01.nupkg, Signed: False
[File] VS.ExternalAPIs.MSBuild.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Conversion.Core.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Engine.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Framework.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Runtime.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Tasks.Core.16.9.0-preview-20622-01.nupkg, Signed: False
[File] Microsoft.Build.Utilities.Core.16.9.0-preview-20622-01.nupkg, Signed: False

Total Time: 00:00:15.8654127
Total Files: 682, Signed: 240, Unsigned: 20, Skipped: 422, Excluded: 0, Skipped & Excluded: 0

```