Small fix for supporting VS2022. (#4089)

## Fixes #4088

Replaces the use of the hardcoded '16.0' string in the Notification package to use the msbuild variable $(VisualStudioVersion).

## PR Type
What kind of change does this PR introduce?

- Bugfix

## What is the current behavior?
Fails to build on VS2022.


## What is the new behavior?
Builds on both VS2019 and VS2022.


## PR Checklist

Please check if your PR fulfills the following requirements:

- [X] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [ ] Sample in sample app has been added / updated (for bug fixes / features)
    - [ ] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [ ] New major technical changes in the toolkit have or will be added to the [Wiki](https://github.com/windows-toolkit/WindowsCommunityToolkit/wiki) e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
- [ ] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [ ] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [X] Contains **NO** breaking changes

Microsoft.Toolkit.Uwp.Notifications/Microsoft.Toolkit.Uwp.Notifications.csproj

@@ -32,7 +32,7 @@
     <CopyLocalLockFileAssemblies Condition="'$(CopyLocalLockFileAssemblies)' == ''">false</CopyLocalLockFileAssemblies>
     <TargetFrameworkIdentifier>.NETCore</TargetFrameworkIdentifier>
     <TargetFrameworkVersion>v5.0</TargetFrameworkVersion>
-    <LanguageTargets>$(MSBuildExtensionsPath)\Microsoft\WindowsXaml\v16.0\Microsoft.Windows.UI.Xaml.CSharp.targets</LanguageTargets>
+    <LanguageTargets>$(MSBuildExtensionsPath)\Microsoft\WindowsXaml\v$(VisualStudioVersion)\Microsoft.Windows.UI.Xaml.CSharp.targets</LanguageTargets>
     <ExtrasImplicitPlatformPackageIsPrivate>true</ExtrasImplicitPlatformPackageIsPrivate>
 
     <!-- Need to override the built-in implicit defines for UAP or it'll be NETCORE5_0. This makes it UAP10_0_10240_0 to match the rest -->