Clean up #12854 a bit

- remove incorrect comment
- do not completely overwrite `$(RestoreAdditionalProjectSources)` values

NuGet.config

@@ -1,5 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
-<!-- Keep this file in sync with src/ProjectTemplates/test/Infrastructure/NuGet.config.in. -->
 <configuration>
   <packageSources>
     <clear />

src/ProjectTemplates/test/Infrastructure/GenerateTestProps.targets

@@ -6,7 +6,7 @@
     Condition="$(DesignTimeBuild) != true">
     <PropertyGroup>
       <PropsProperties>
-        RestoreAdditionalProjectSources=$([MSBuild]::Escape("$(ArtifactsShippingPackagesDir);$(ArtifactsNonShippingPackagesDir)"));
+        RestoreAdditionalProjectSources=$([MSBuild]::Escape("$(RestoreAdditionalProjectSources);$(ArtifactsShippingPackagesDir);$(ArtifactsNonShippingPackagesDir)"));
         MicrosoftNetCompilersToolsetPackageVersion=$(MicrosoftNetCompilersToolsetPackageVersion);
         MicrosoftNETCoreAppRuntimeVersion=$(MicrosoftNETCoreAppRuntimeVersion);
         MicrosoftNETCoreAppRefPackageVersion=$(MicrosoftNETCoreAppRefPackageVersion);

src/SiteExtensions/LoggingAggregate/src/Microsoft.AspNetCore.AzureAppServices.SiteExtension/Microsoft.AspNetCore.AzureAppServices.SiteExtension.csproj

@@ -17,7 +17,7 @@
     <NoSemVer20>true</NoSemVer20>
 
     <!-- Grab packages LB.csproj should have just built. -->
-    <RestoreAdditionalProjectSources>$(ArtifactsNonShippingPackagesDir)</RestoreAdditionalProjectSources>
+    <RestoreAdditionalProjectSources>$(RestoreAdditionalProjectSources);$(ArtifactsNonShippingPackagesDir)</RestoreAdditionalProjectSources>
   </PropertyGroup>
 
   <ItemGroup>

src/SiteExtensions/Sdk/SiteExtension.targets

@@ -15,6 +15,7 @@
       <_RuntimeStoreManifestFile>$(_DepsOutputDirectory)\rs.csproj</_RuntimeStoreManifestFile>
       <_RuntimeStoreOutput>$(_DepsOutputDirectory)\rs\</_RuntimeStoreOutput>
       <_RsRestoreSources>
+        $(RestoreAdditionalProjectSources);
         $(ArtifactsShippingPackagesDir);
         $(ArtifactsNonShippingPackagesDir)
       </_RsRestoreSources>