CI: run unittests with beta cython

Author: black-sliver

.github/workflows/unittests.yml

@@ -32,6 +32,8 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
+        cython:
+          - stable
         python:
           - {version: '3.8'}
           - {version: '3.9'}
@@ -43,13 +45,21 @@ jobs:
             os: windows-latest
           - python: {version: '3.10'}  # current
             os: macos-latest
+          - python: {version: '3.10'}  # current
+            os: ubuntu
+            cython: beta
 
     steps:
     - uses: actions/checkout@v3
     - name: Set up Python ${{ matrix.python.version }}
       uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python.version }}
+    - name: Install cython beta
+      if: ${{ matrix.cython == 'beta' }}
+      run: |
+        python -m pip install --upgrade pip
+        python -m pip install --pre --upgrade cython
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip