Fix and clean up CI script (#876)

* Split Python 2.7 tests from Python 3 tests as they use different paths
  and require installation of the typing module.
* Split running typing and typing_extensions tests into two steps.
* Don't test typing on Python 3
* Remove pytest-xdist and pytest-cov not necessary here

Author: srittau

.github/workflows/ci.yml

@@ -8,14 +8,38 @@ permissions:
   contents: read
 
 jobs:
+  tests-27:
+    name: Run tests (2.7)
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 2.7
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r test-requirements.txt
+
+      - name: Test typing
+        run: pytest python2
+
+      - name: Test typing_extensions
+        run: |
+          pip install typing
+          pytest typing_extensions/src_py2
+
   tests:
     name: Run tests
 
     strategy:
       fail-fast: false
       matrix:
-        # Python 3.4 disabled, due to problems with GitHub Actions.
-        python-version: [3.10-dev, 3.9, 3.8, 3.7, 3.6, 3.5, 2.7]
+        python-version: [3.10-dev, 3.9, 3.8, 3.7, 3.6]
 
     runs-on: ubuntu-latest
 
@@ -40,16 +64,8 @@ jobs:
           pip install --upgrade pip
           pip install -r test-requirements.txt
 
-      - name: Run tests
-        env:
-          PYTHON_VERSION: ${{ matrix.python-version }}
-        run: |
-          export PYTHONPATH=`python -c "import sys; print('python2' if sys.version.startswith('2') else 'src')"`
-          if [[ $PYTHON_VERSION < '3.7' ]]; then pytest $PYTHONPATH; fi
-
-          if [[ $PYTHON_VERSION < '3.5' ]]; then pip install -U .; fi
-          export PYTHONPATH=`python -c "import sys; print('typing_extensions/src_py2' if sys.version.startswith('2') else 'typing_extensions/src_py3')"`
-          pytest $PYTHONPATH
+      - name: Test typing_extensions
+        run: pytest typing_extensions/src_py3
 
   linting:
     name: Lint