Bump dotnet SDK version for github actions "test" workflow.

Author: ignatz

.github/workflows/test.yml

@@ -28,10 +28,10 @@ jobs:
         with:
           channel: stable
           flutter-version: 3.24.3
-      - name: Setup .NET 8.x
-        uses: actions/setup-dotnet@v3
+      - name: Setup .NET SDK
+        uses: actions/setup-dotnet@v4
         with:
-          dotnet-version: '8.x'
+          dotnet-version: '9.x'
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable