Bump System.Resources.Extensions from 6.0.0 to 8.0.0

Bumps [System.Resources.Extensions](https://github.com/dotnet/runtime) from 6.0.0 to 8.0.0.
- [Release notes](https://github.com/dotnet/runtime/releases)
- [Commits](dotnet/runtime@v6.0.0...v8.0.0)

---
updated-dependencies:
- dependency-name: System.Resources.Extensions
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

src/Ookii.Dialogs.WinForms/Ookii.Dialogs.WinForms.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>net6.0-windows;net5.0-windows;netcoreapp3.1;net462</TargetFrameworks>
     <UseWindowsForms>true</UseWindowsForms>
@@ -50,7 +50,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="System.Resources.Extensions" Version="6.0.0" />
+    <PackageReference Include="System.Resources.Extensions" Version="8.0.0" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
   </ItemGroup>