fix to include .targets file to both 'build' and 'buildMultitargeting'

Author: smdn

src/Smdn.Reflection.ReverseGenerating.ListApi.MSBuild.Tasks/GenerateMSBuildTargetsFile.targets

@@ -51,6 +51,7 @@ SPDX-License-Identifier: MIT
     />
 
     <ItemGroup>
+      <None Pack="true" Include="$(GenerateMSBuildTargetsFileOutputPath)" PackagePath="build" />
       <None Pack="true" Include="$(GenerateMSBuildTargetsFileOutputPath)" PackagePath="buildMultitargeting" />
     </ItemGroup>
   </Target>