use bash shell

Author: basnijholt

.github/workflows/tox.yml

@@ -22,6 +22,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Set Python version for tox
       run: echo "PY_VERSION=$(echo py${version//./})" >> $GITHUB_ENV
+      shell: bash
       env:
         version: ${{ matrix.python-version }}
     - name: Register Python problem matcher