Fixed Nunit upgrade

Author: gigi81

.editorconfig

@@ -9,3 +9,7 @@ end_of_line = CRLF
 [*.cs]
 indent_style = space
 indent_size = 4
+
+dotnet_diagnostic.NUnit2003.severity = suggestion
+dotnet_diagnostic.NUnit2004.severity = suggestion
+dotnet_diagnostic.NUnit2005.severity = suggestion

Directory.Build.props

@@ -9,7 +9,6 @@
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
-    <LangVersion>9.0</LangVersion>
     <PackageTags>testing</PackageTags>
     <PackageProjectUrl>https://github.com/System-IO-Abstractions/System.IO.Abstractions.Extensions</PackageProjectUrl>
     <RepositoryUrl>https://github.com/System-IO-Abstractions/System.IO.Abstractions.Extensions.git</RepositoryUrl>

src/System.IO.Abstractions.Extensions/System.IO.Abstractions.Extensions.csproj

@@ -6,6 +6,7 @@
 		<Description>Convenience functionalities on top of System.IO.Abstractions</Description>
 		<RootNamespace>System.IO.Abstractions</RootNamespace>
 		<PackageReleaseNotes>$([System.IO.File]::ReadAllText("$(MSBuildProjectDirectory)/../../ReleaseNotes.md"))</PackageReleaseNotes>
+		<LangVersion>9.0</LangVersion>
 	</PropertyGroup>
 
 	<ItemGroup>

tests/System.IO.Abstractions.Extensions.Tests/.editorconfig

@@ -7,6 +7,14 @@
 		<IsTestable>true</IsTestable>
 	</PropertyGroup>
 
+	<ItemGroup>
+		<Using Include="NUnit.Framework.Legacy.ClassicAssert" Alias="Assert" />
+	</ItemGroup>
+	
+	<ItemGroup>
+		<ProjectReference Include="..\..\src\System.IO.Abstractions.Extensions\System.IO.Abstractions.Extensions.csproj" />
+	</ItemGroup>
+	
 	<ItemGroup>
 		<PackageReference Include="TestableIO.System.IO.Abstractions.Wrappers" Version="22.0.10" />
 		<PackageReference Include="NUnit" Version="4.3.2" />
@@ -16,7 +24,6 @@
 		<PackageReference Include="coverlet.collector" Version="6.0.4" />
 		<PackageReference Include="GitHubActionsTestLogger" Version="2.4.1" />
 		<PackageReference Include="Snapshooter.NUnit" Version="1.0.1" />
-		<ProjectReference Include="..\..\src\System.IO.Abstractions.Extensions\System.IO.Abstractions.Extensions.csproj" />
 	</ItemGroup>
 
 </Project>