Test 3.10-dev on all OS on GHA

Author: hugovk

.github/workflows/test.yml

@@ -8,35 +8,25 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["pypy3", "3.6", "3.7", "3.8", "3.9"]
+        python-version: ["pypy3", "3.6", "3.7", "3.8", "3.9", "3.10-dev"]
         os: [ubuntu-latest, macos-latest, windows-latest]
         include:
           # Include new variables for Codecov
           - { codecov-flag: GHA_Ubuntu, os: ubuntu-latest }
           - { codecov-flag: GHA_macOS, os: macos-latest }
           - { codecov-flag: GHA_Windows, os: windows-latest }
-          # Dev versions
-          - { python-version: 3.10-dev, os: ubuntu-18.04 }
 
     steps:
       - uses: actions/checkout@v2
 
-      - name: Set up Python ${{ matrix.python }} (deadsnakes)
-        uses: deadsnakes/action@v1.0.0
-        if: endsWith(matrix.python-version, '-dev')
-        with:
-          python-version: ${{ matrix.python-version }}
-
       - name: Set up Python ${{ matrix.python-version }}
-        if: "!endsWith(matrix.python-version, '-dev')"
         uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}
 
       - name: Get pip cache dir
         id: pip-cache
         run: |
-          python -m pip install -U "pip>=20.1"
           echo "::set-output name=dir::$(pip cache dir)"
 
       - name: pip cache