Bump Microsoft.CodeAnalysis.CSharp from 4.7.0 to 4.8.0 in /src/GirTool

Bumps [Microsoft.CodeAnalysis.CSharp](https://github.com/dotnet/roslyn) from 4.7.0 to 4.8.0.
- [Release notes](https://github.com/dotnet/roslyn/releases)
- [Changelog](https://github.com/dotnet/roslyn/blob/main/docs/Breaking%20API%20Changes.md)
- [Commits](https://github.com/dotnet/roslyn/commits)

---
updated-dependencies:
- dependency-name: Microsoft.CodeAnalysis.CSharp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

src/Generation/Generator/Generator.csproj

@@ -4,6 +4,6 @@
     </PropertyGroup>
     <ItemGroup>
       <ProjectReference Include="..\GirModel\GirModel.csproj" />
-      <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.7.0" />
+      <PackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="4.8.0" />
     </ItemGroup>
 </Project>