CmdPal: Add trailing backslash to OutDir in Microsoft.Terminal.UI project file (#45250)

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## Summary of the Pull Request

Ensures the OutDir path in Microsoft.Terminal.UI.vcxproj ends with a
backslash, making it explicit as a directory, and fixes warning MSB8004.


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src/modules/cmdpal/Microsoft.Terminal.UI/Microsoft.Terminal.UI.vcxproj

@@ -201,7 +201,7 @@
     <None Include="Microsoft.Terminal.UI.def" />
   </ItemGroup>
   <PropertyGroup>
-    <OutDir>..\..\..\..\$(Platform)\$(Configuration)\WinUI3Apps\CmdPal</OutDir>
+    <OutDir>..\..\..\..\$(Platform)\$(Configuration)\WinUI3Apps\CmdPal\</OutDir>
     <IntDir>obj\$(Platform)\$(Configuration)\</IntDir>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />