Update CI-unixish.yml: trying to not upgrade pip

Author: Tal500

.github/workflows/CI-unixish.yml

@@ -39,7 +39,6 @@ jobs:
     - name: Install missing Python packages
       run: |
         python3 -m pip config set global.break-system-packages true
-        python3 -m pip install pip --upgrade
         python3 -m pip install pytest
 
     - name: make simplecpp