setup-action: install pytest.

setup-action/action.yml

@@ -19,6 +19,10 @@ runs:
       python-version: '3.12'
       cache: pip
 
+  - name: Install pytest
+    run: pip install pytest
+    shell: bash
+
   - name: Install niar
     run: cd setup-niar-out/niar && pip install -e .
     shell: bash