Change default .NET version to 9.x

Updated default .NET versions to 9.x.

Author: BenjaminMichaelis

.github/actions/setup-dotnet-build/action.yml

@@ -5,8 +5,7 @@ inputs:
     description: '.NET versions to install'
     required: false
     default: |
-      3.1.x
-      6.x
+      9.x
   configuration:
     description: 'Build configuration'
     required: false
@@ -30,4 +29,4 @@ runs:
 
     - name: Build
       run: dotnet build --configuration ${{ inputs.configuration }} ${{ inputs.build-args }}
-      shell: pwsh
+      shell: pwsh