ci: Install Python dependencies including PyTorch for GraphSAGE tests

- Add Python 3.9 setup step using actions/setup-python@v4
- Install requirements from geaflow-dsl-plan/src/main/resources/requirements.txt
- Include pip cache to speed up subsequent builds
- Verify torch installation with pip list
- Enable full GraphSAGE integration tests in CI

This ensures all Python dependencies (torch, numpy, etc.) are available
for running the GraphSAGE integration tests, preventing ModuleNotFoundError
failures in CI.

Author: kitalkuyo-gita

.github/workflows/ci.yml

@@ -77,5 +77,17 @@ jobs:
         with:
           version: "21.7"
 
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.9'
+          cache: 'pip'
+
+      - name: Install Python dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r geaflow/geaflow-dsl/geaflow-dsl-plan/src/main/resources/requirements.txt
+          pip list | grep -i torch
+
       - name: Build and Test On JDK 8
         run: mvn -B -e clean test -Pjdk8 -Duser.timezone=Asia/Shanghai -Dlog4j.configuration="log4j.rootLogger=WARN, stdout"