Workaround harmless MSBuild warning in VS (#2350)

Author: Evangelink

src/Adapter/Build/Common/MSTest.TestAdapter.targets

@@ -31,9 +31,20 @@
       (i.e. `<None Remove="@(TestAdapterContent)" />`)
       -->
     <None Include="@(TestAdapterContent)" />
-    <Reference Include="Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter" HintPath="$(MSBuildThisFileDirectory)Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.dll" Condition=" '$(EnableMSTestRunner)' == 'true' " />
   </ItemGroup>
 
+  <Choose>
+    <!-- Avoid false warning about missing reference (msbuild bug) -->
+    <!-- https://github.com/dotnet/msbuild/issues/9698#issuecomment-1945763467 -->
+    <When Condition=" '$(EnableMSTestRunner)' == 'true' ">
+      <ItemGroup>
+        <Reference Include="Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter">
+          <HintPath>$(MSBuildThisFileDirectory)Microsoft.VisualStudio.TestPlatform.MSTest.TestAdapter.dll</HintPath>
+        </Reference>
+      </ItemGroup>
+    </When>
+  </Choose>
+
   <Target Name="GetMSTestV2CultureHierarchy">
     <!--
       Only traversing 5 levels in the culture hierarchy. This is the maximum length for all cultures and should be sufficient