Enable testing on 3.10-dev

Author: mgorny

.github/workflows/ci.yml

@@ -10,7 +10,10 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-20.04, windows-2019, macos-10.15]
-        python-version: [ '3.6', '3.7', '3.8', '3.9', 'pypy-3.6', 'pypy-3.7' ]
+        python-version: [ '3.6', '3.7', '3.8', '3.9', '3.10-dev', 'pypy-3.6', 'pypy-3.7' ]
+        exclude:
+          - os: windows-2019
+            python-version: 3.10-dev
     steps:
     - uses: actions/checkout@v2
       with:
@@ -19,6 +22,8 @@ jobs:
       uses: actions/setup-python@v2
       with:
         python-version: ${{ matrix.python-version }}
+    - name: Install wheel
+      run: pip install wheel
     - name: Build package
       run: python setup.py install
     - name: Run tests