make test work with python 2

Author: PhilipVinc

.github/workflows/system.yml

@@ -72,6 +72,9 @@ jobs:
           version: ${{ matrix.julia-version }}
           arch: ${{ matrix.architecture }}
           show-versioninfo: true
+      - name: Set PYTHON Env variable
+        run: echo "PYTHON=python" >> $GITHUB_ENV
+        if: ${{ matrix.python-version != '2.7' }}
       - name: Install PyPreferences
         shell: julia --project=@. {0}
         run: |