fix shell execution

Author: cav71

.github/workflows/python.yaml

@@ -25,13 +25,15 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
       - name: Install dependencies
+        shell: bash
         run: |
           python -m pip install --upgrade pip
           pip install Pygments>=2.5.2 pytest pytest-cov pytest-html
       - name: Test
         env:
           PYTHONPATH: lib
           OUTDIR: build/qa-${{ matrix.python-version }}-${{ matrix.os }}
+        shell: bash
         run: |
           py.test \
             --cov=markdown2 \