GHA: use Java 11 on Windows

* in order to fix build errors:
  error XA0031: Java SDK 11.0 or above is required when using .NET 6 or higher.
  Download the latest JDK at: https://aka.ms/msopenjdk
  [D:\a\oxyplot-maui\oxyplot-maui\Source\OxyPlot.Maui.Skia\OxyPlot.Maui.Skia.csproj::TargetFramework=net7.0-android33.0]

.github/workflows/dotnet.yml

@@ -21,6 +21,11 @@ jobs:
       uses: actions/setup-dotnet@v3
       with:
         dotnet-version: 7.0.x
+    - name: Set up JDK 11
+      uses: actions/setup-java@v3
+      with:
+        distribution: 'temurin'
+        java-version: '11'
     - name: Install .NET MAUI
       shell: pwsh
       run: |