Update WFCrossThreadCS.csproj from .NET Framework net452 to LTS (or current) version

[github-actions[bot]]

The WFCrossThreadCS.csproj project file targets a .NET version which is no longer supported. This is an auto-generated issue, detailed and discussed in dotnet/docs#22271.

See line 12 in samples/snippets/csharp/VS_Snippets_CLR_System/system.Invalidoperationexception.threading.wf/cs/WFCrossThreadCS.csproj.

Target version	End of life	Release notes	Nearest LTS TFM version
v4.5.2	N/A	v4.5.2 release notes	net48

Consider upgrading the project to either the current release, or the nearest LTS TFM version.

If this project is intentionally targeting an unsupported version, you can optionally configure to ignore this automated issue. Create a file at the root of the repository, named dotnet-versionsweeper.json and add an ignore entry following the globbing patterns detailed here.

{
    "ignore": [
        "**/samples/snippets/csharp/VS_Snippets_CLR_System/system.Invalidoperationexception.threading.wf/cs/WFCrossThreadCS.csproj"
    ]
}

[dotnet-issue-labeler[bot]]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.