fix: use GitHub secret for lock-threads action

.github/workflows/main.yml

@@ -0,0 +1,34 @@
+name: Main Workflow
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.x'
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+
+      - name: Run tests
+        run: pytest
+
+      - name: Lock threads
+        uses: dessant/lock-threads@v4
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}