Use Java 21 on Windows GHA runners

Author: khaeru

.github/workflows/pytest.yaml

@@ -156,6 +156,13 @@ jobs:
       # Work around ts-graphviz/setup-graphviz#630
       if: matrix.os != 'macos-13'
 
+    - name: Set Java version on Windows
+      if: startsWith(matrix.os, 'windows-')
+      uses: actions/setup-java@v4
+      with:
+        distribution: temurin
+        java-version: '21'
+
     - name: Install packaging
       run: uv pip install packaging