workflow: install python3-pytest too to workaround test_host.py

The test_host.py:test_signals_on_separate_fd (and more)  runs
itself but that run will happen without the tox env so a pip/tox
installed pytest will not be found, install the pytest package
as a workaround.

.github/workflows/test.yml

@@ -83,7 +83,10 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: actions/setup-python@v5
-    - run: sudo apt install -y tox
+      # the test_host.py:test_signals_on_separate_fd runs itself but that
+      # run will happen without the tox env so a pip/tox installed pytest
+      # will not be found, install the pytest package as a workaround
+    - run: sudo apt install -y tox python3-pytest
     - name: "Run as user on default runer"
       run: |
         # depsolve tests tend to be slow but are easy to parallize