CI-unixish.yml: use Python version provided by platform

Author: firewave

.github/workflows/CI-unixish.yml

@@ -17,11 +17,6 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
-      - name: Set up Python 3.10
-        uses: actions/setup-python@v2
-        with:
-          python-version: '3.10'
-
       - name: Install missing software on ubuntu
         if: contains(matrix.os, 'ubuntu')
         run: |
@@ -38,7 +33,7 @@ jobs:
       - name: Install missing software on macos
         if: contains(matrix.os, 'macos')
         run: |
-          brew install coreutils z3 qt@5
+          brew install coreutils python3 z3 qt@5
 
       - name: Install missing Python packages
         run: |