ci(github-actions): add test workflow for backend python code

新增GitHub Actions测试工作流，在push和pull request到main分支且后端Python文件变更时运行后端单元测试

.github/workflows/test.yml

@@ -0,0 +1,34 @@
+name: Test
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'backend/**/*.py'
+  pull_request:
+    branches: [main]
+
+jobs:
+  test-channels:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+        with:
+          version: "0.7.2"
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Install dependencies
+        run: uv sync --group test
+
+      - name: Run channel gateway tests
+        run: uv run pytest test/unit/channels/ -v --tb=short