explicitly run this step in Git bash

Author: mshafer-NI

.github/workflows/PR.yml

@@ -55,11 +55,13 @@ jobs:
       - name: Run tests
         run: poetry run pytest -v
       - name: Install package into separate venv
+        shell: bash
         run: |
           python3 -m venv test_venv
           . test_venv/bin/activate || call test_venv\Scripts\activate
           pip install .
       - name: Lint our own pakage
+        shell: bash
         run: |
           . test_venv/bin/activate || call test_venv\Scripts\activate
           nps lint .