Add check workflow for python 3.8

Fix #49

.github/workflows/python38.yml

@@ -0,0 +1,72 @@
+name: Check and test transferwee
+
+'on':
+  push:
+    branches:
+      - master
+  pull_request:
+  schedule:
+    - cron: '0 0 * * *'
+
+jobs:
+  build:
+    name: Check and test transferwee
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.8'
+      - name: Cache pip
+        uses: actions/cache@v3
+        with:
+          # This path is specific to Ubuntu
+          path: ~/.cache/pip
+          # Look to see if there is a cache hit for the corresponding
+          # requirements file
+          key: ${{ runner.os }}-pip-${{ hashFiles('requirements.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
+            ${{ runner.os }}-
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install black
+          pip install flake8
+          pip install mypy
+          pip install requests
+      - name: Lint with flake8
+        run: |
+          # stop the build if there are Python syntax errors or undefined names
+          flake8 . --select=E9,F63,F7,F82 --show-source
+          # exit-zero treats all errors as warnings.
+          flake8 . --exit-zero --max-complexity=10
+      - name: Check code style via Black
+        run: |
+          black --check .
+      - name: Static type checking via mypy
+        run: |
+          mypy --non-interactive --install-types .
+          mypy --strict --disable-error-code no-any-return .
+      - name: Test transferwee
+        shell: bash
+        env:
+          PYTHONDEVMODE: 1
+          PYTHONTRACEMALLOC: 1
+        run: |
+          sleep_time=1
+          factor=2
+          cd tests
+          until ./check.sh ; do
+            e=$?
+            if [ "${sleep_time}" -gt 64 ]; then
+              echo "Tried too much times"
+              exit $e
+            fi
+            echo "Tests failed with exit code ${e}"
+            echo "Retrying in ${sleep_time}"
+            sleep ${sleep_time}
+            sleep_time=$((sleep_time * factor))
+          done