[CONFIG] [Github Actions] Multiple .NET framework versions

Author: Gonzalo Diaz

.github/workflows/dotnet.yml

@@ -21,13 +21,14 @@ jobs:
       fail-fast: false
       matrix:
         os: ["windows-2022", "ubuntu-24.04", "macos-14"]
+        dotnet-version: [8.0.x, 9.0.x]
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v4
-      - name: Setup .NET
+      - name: Setup .NET ${{ matrix.dotnet-version }}
         uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: 8.0.x
+          dotnet-version: ${{ matrix.dotnet-version }}
       - name: Restore dependencies
         run: dotnet restore
       - name: Build

src/algorithm_exercises_csharp/algorithm_exercises_csharp.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFramework>net8.0;net9.0</TargetFramework>
     <RootNamespace>algorithm_exercises_csharp</RootNamespace>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>