Try to let vsix override the langversion with one msbuild 17 can handle

Author: GrahamTheCoder

.github/workflows/dotnet.yml

@@ -35,7 +35,7 @@ jobs:
     - name: Add msbuild to PATH
       uses: microsoft/setup-msbuild@v2
       with:
-       vs-version: '[18.0,)'
+       vs-version: '[17.0,)'
 
     - name: Dotnet deterministic Build
       run:  dotnet build DotNetBuildable.slnf /p:Platform=$env:BuildPlatform /p:Configuration=$env:BuildTarget /p:ContinuousIntegrationBuild=true

Directory.Build.props

@@ -7,12 +7,12 @@
     <WarningsNotAsErrors>$(WarningsNotAsErrors);NU1605;NU1701;NU1901;NU1902;NU1903;NU1904;NU1510;NU1903</WarningsNotAsErrors>
     <WarningLevel>4</WarningLevel>
     <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
-    <LangVersion>14.0</LangVersion>
+    <LangVersion Condition="'$(LangVersion)' == ''">14.0</LangVersion>
     <AssemblyVersion>10.0.0.0</AssemblyVersion>
     <FileVersion>10.0.0.0</FileVersion>
     <Version>10.0.0</Version>
     <Authors>ICSharpCode</Authors>
     <Copyright>Copyright (c) 2017-2023 AlphaSierraPapa for the CodeConverter team</Copyright>
     <Company>ICSharpCode</Company>
   </PropertyGroup>
-</Project>
+</Project>

Vsix/Vsix.csproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="15.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <MinimumVisualStudioVersion>16.0</MinimumVisualStudioVersion>
@@ -24,7 +24,7 @@
     <SignAssembly>false</SignAssembly>
     <DeployExtension Condition="'$(BuildingInsideVisualStudio)' != 'true'">False</DeployExtension>
     <RuntimeIdentifiers>win</RuntimeIdentifiers>
-    <LangVersion>9.0</LangVersion>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
   <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
@@ -162,4 +162,4 @@
   <Target Name="AfterBuild">
   </Target>
   -->
-</Project>
+</Project>