Adding PEP8/flake8 GitHub Action

.flake8

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+[flake8]
+exclude = .git,__pycache__,migrations
+max-line-length = 120

.github/workflows/pep8.yml

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+name: PEP8 Check
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  flake8:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.x
+
+      - name: Install dependencies
+        run: pip install flake8
+
+      - name: Run flake8
+        run: flake8