Freeze tests for Python 3.8/Ubuntu 20.04

.github/workflows/pytest-frozen-ubuntu-20.04.yml

@@ -0,0 +1,52 @@
+name: Python tests
+# This workflow is triggered on pushes and PRs to the repository.
+# Only run if we changed a Python file
+on:
+  push:
+    branches:
+      - dev
+  pull_request:
+  release:
+    types: [published]
+
+# Cancel if a newer run is started
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  pytest:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v3
+        name: Check out source-code repository
+
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v3
+        with:
+          python-version: "3.8"
+
+      - name: Install python dependencies
+        run: |
+          python -m pip install --upgrade pip -r requirements-dev.txt
+          pip install -e .
+
+      - name: Downgrade git to the Ubuntu official repository's version
+        run: |
+          sudo apt remove git git-man
+          sudo add-apt-repository --remove ppa:git-core/ppa
+          sudo apt install git
+
+      - name: Install Nextflow
+        uses: nf-core/setup-nextflow@v1
+        with:
+          version: "latest-everything"
+
+      - name: Test with pytest
+        run: python3 -m pytest tests/ --color=yes --cov-report=xml --cov-config=.github/.coveragerc --cov=nf_core
+
+      - uses: codecov/codecov-action@v1
+        name: Upload code coverage report
+        with:
+          if: success()
+          token: ${{ secrets.CODECOV_TOKEN }}