WinFormsTestApp: purge stale lock/obj to drop Microsoft.WindowsDesktop.App.Ref 3.1.0 (fix CG Critical from #5482) (#5506)

Disable lockfiles for WinForms test application

Author: gladjohn

tests/devapps/WinFormsTestApp/WinFormsTestApp.csproj

@@ -10,6 +10,8 @@
     <RuntimeIdentifiers>win-x86;win-x64;win-arm64</RuntimeIdentifiers>
     <Nullable>enable</Nullable>
     <LangVersion>latest</LangVersion>
+    <!-- Avoid sticky lockfiles for this test app -->
+    <RestorePackagesWithLockFile>false</RestorePackagesWithLockFile>
   </PropertyGroup>
 
   <!-- Platform-specific configurations -->