[BUG]: DotNetCoreCLI@2 breaks package source mappings for internal feeds when using a nuget.config file

[cdavis-elekta]

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Task name

DotNetCoreCLI

Task version

2

Issue Description

The DotNetCoreCLI task's restore command prepends feed- to a package source key for each private (internal) feed it discovers in a nuget.config file stored in the source repo (i.e., when the nugetConfigPath task input is set) but DOES NOT prepend feed- to the same key in a package source mapping element, effectively breaking package source mapping.

I have replaced the actual private feed information with example in the nuget.config file shown below and the logs.

<configuration>
  <packageSources>
    <clear/>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json"/>
    <add key="example" value="https://pkgs.dev.azure.com/Example/project/_packaging/example/nuget/v3/index.json"/>
  </packageSources>
  <packageSourceMapping>
    <packageSource key="nuget.org">
      <package pattern="*"/>
    </packageSource>
    <packageSource key="example">
      <package pattern="Example.*"/>
    </packageSource>
  </packageSourceMapping>
</configuration>
`

This results in "Package source mapping match not found for package ID 'Example.Package'" errors and can result in restore failures

To work around this bug, I had to prepend `feed-` to the package source element with the key `example` in the nuget.config in the source repository, as follows:

```xml
<configuration>
  <packageSources>
    <clear/>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json"/>
    <add key="example" value="https://pkgs.dev.azure.com/Example/project/_packaging/example/nuget/v3/index.json"/>
  </packageSources>
  <packageSourceMapping>
    <packageSource key="nuget.org">
      <package pattern="*"/>
    </packageSource>
    <packageSource key="feed-example">
      <package pattern="Example.*"/>
    </packageSource>
  </packageSourceMapping>
</configuration>
`

### Environment type (Please select at least one enviroment where you face this issue)

- [ ] Self-Hosted
- [x] Microsoft Hosted
- [ ] VMSS Pool
- [ ] Container

### Azure DevOps Server type

dev.azure.com (formerly visualstudio.com)

### Azure DevOps Server Version (if applicable)

N/A

### Operation system

N/A

### Relevant log output

```shell
Output extracted from dotnet restore run by the task with `verbosityRestore: Detailed` task input:

Restoring packages for .NETCoreApp,Version=v8.0...
         Package source mapping match not found for package ID 'Example.Package'.
         Package source mapping matches found for package ID 'Microsoft.NET.Test.Sdk' are: 'nuget.org'.

Full task logs with system.debug enabled

##[debug]Setting up sources ##[debug]selectOrConfig=config ##[debug]nugetConfigPath=/__w/6/s/src/nuget.config ##[debug]check path : /__w/6/s/src/nuget.config ##[debug]nugetConfigPath=/__w/6/s/src/nuget.config ##[debug]Absolute path for pathSegments: /__w/6/s/src/nuget.config = /__w/6/s/src/nuget.config ##[debug]build.sourcesDirectory=/__w/6/s ##[debug]Absolute path for pathSegments: /__w/6/s = /__w/6/s ##[debug]nugetConfigPathpath supplied :true ##[debug]Agent.BuildDirectory=/__w/6 ##[debug]build.buildId=1000000 ##[debug]Setting auth in the temp nuget.config ##[debug]Saving NuGet.config to a temporary config file. ##[debug]Getting sources from NuGet.config in this location: /__w/6/Nuget/tempNuGet_1004187.config ##[debug]considering source https://api.nuget.org/v3/index.json. Internal: false ##[debug]No external auth information ##[debug]considering source https://pkgs.dev.azure.com/Example/project/_packaging/example/nuget/v3/index.json. Internal: true ##[debug]Setting auth for internal source https://pkgs.dev.azure.com/Example/project/_packaging/example/nuget/v3/index.json ##[debug]Prefixing internal source feed name example with feed- ##[debug]ValidAuthenticationTypes_feed-example=undefined ##[debug]which 'dotnet' ##[debug]found: '/__t/dotnet/dotnet' ##[debug]restoreArguments=undefined ##[debug]which '/__t/dotnet/dotnet' ##[debug]found: '/__t/dotnet/dotnet' ##[debug]/__t/dotnet/dotnet arg: restore ##[debug]/__t/dotnet/dotnet arg: /__w/6/s/src/Example.sln ##[debug]/__t/dotnet/dotnet arg: --configfile ##[debug]/__t/dotnet/dotnet arg: /__w/6/Nuget/tempNuGet_1004187.config ##[debug]/__t/dotnet/dotnet arg: --verbosity ##[debug]/__t/dotnet/dotnet arg: Detailed

Repro steps

1. Commit a nuget.config file with a package source and package source mapping configured for a private/internal NuGet feed (i.e., Azure Artifacts feed) to a repository in Azure DevOps.  Use the name of the feed for the package source and package source mapping key.
2. In a YAML pipeline, add a NuGetAuthenticate@1 step followed by a DotNetCoreCLI@2 step for the "restore" command with the `nugetConfigPath` input set to the path of the nuget.config in the repo (e.g., "src\nuget.config").  Set the `verbosityRestore` input to "Detailed".
3. Run the pipeline.

Expected results:
Packages in the private/internal feed are successfully restored.

Actual results:
Packages (which aren't already cached by the Agent) in the private/internal feed are not restored.  The `dotnet restore` output includes `Package source mapping match not found for package ID '...' log entries.