Don't reference System.ValueTuple on netstandard2.0 (#63240)

It's not needed there and will raise a NuGet package pruning warning

Author: akoeplinger

src/Logging.AzureAppServices/src/Microsoft.Extensions.Logging.AzureAppServices.csproj

@@ -18,7 +18,7 @@
     <Reference Include="Microsoft.Extensions.Logging.Abstractions" />
     <Reference Include="Microsoft.Extensions.Logging.Configuration" />
     <Reference Include="Microsoft.Extensions.Logging" />
-    <Reference Include="System.ValueTuple" Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'" />
+    <Reference Include="System.ValueTuple" Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == '$(DefaultNetFxTargetFramework)' OR '$(MSBuildRestoreSessionId)' == ''">

src/Testing/src/Microsoft.AspNetCore.InternalTesting.csproj

@@ -28,7 +28,7 @@
     <Reference Include="Microsoft.Extensions.Logging" />
     <Reference Include="Serilog.Extensions.Logging" />
     <Reference Include="Serilog.Sinks.File" />
-    <Reference Include="System.ValueTuple" Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'" />
+    <Reference Include="System.ValueTuple" Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'" />
 
     <!--
       This intentionally does not reference 'xunit', 'xunit.core', or any runner packages.