build: on push GitHub Action to lint Python code

Blocked by: #1929

.github/workflows/push.yml

@@ -0,0 +1,24 @@
+name: on push
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      max-parallel: 2
+      matrix:
+        python-version: [2.7, 3.7]
+    steps:
+    - uses: actions/checkout@v1
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r requirements.txt
+    - name: Lint with flake8
+      run: |
+        pip install flake8
+        flake8 --version
+        flake8 .