Fix MSBuild property name for MicrosoftBuildTasksCoreVersion (#37404)

There was a missing 's', which caused source-build to use a pre-built when building.

eng/Versions.props

@@ -180,7 +180,7 @@
     <MicrosoftBuildVersion>16.9.0</MicrosoftBuildVersion>
     <MicrosoftAzureSignalRVersion>1.2.0</MicrosoftAzureSignalRVersion>
     <MicrosoftBuildFrameworkVersion>16.9.0</MicrosoftBuildFrameworkVersion>
-    <MicrosoftBuildTaskCoreVersion>16.9.0</MicrosoftBuildTaskCoreVersion>
+    <MicrosoftBuildTasksCoreVersion>16.9.0</MicrosoftBuildTasksCoreVersion>
     <MicrosoftBuildUtilitiesCoreVersion>16.9.0</MicrosoftBuildUtilitiesCoreVersion>
     <MicrosoftBuildLocatorVersion>1.2.6</MicrosoftBuildLocatorVersion>
     <MicrosoftBuildUtilitiesCoreVersion>16.9.0</MicrosoftBuildUtilitiesCoreVersion>

eng/tools/RepoTasks/RepoTasks.csproj

@@ -21,7 +21,7 @@
 
   <ItemGroup Condition="'$(TargetFramework)' == '$(DefaultNetCoreTargetFramework)'">
     <PackageReference Include="Microsoft.Build.Framework" Version="$(MicrosoftBuildFrameworkVersion)" />
-    <PackageReference Include="Microsoft.Build.Tasks.Core" Version="$(MicrosoftBuildTaskCoreVersion)" />
+    <PackageReference Include="Microsoft.Build.Tasks.Core" Version="$(MicrosoftBuildTasksCoreVersion)" />
     <PackageReference Include="Microsoft.Build.Utilities.Core" Version="$(MicrosoftBuildUtilitiesCoreVersion)" />
   </ItemGroup>