CI: cap pytest-subtest version (#4344)

.github/workflows/unittests.yml

@@ -53,7 +53,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install pytest pytest-subtests pytest-xdist
+        pip install pytest "pytest-subtests<0.14.0" pytest-xdist
         python ModuleUpdate.py --yes --force --append "WebHostLib/requirements.txt"
         python Launcher.py --update_settings  # make sure host.yaml exists for tests
     - name: Unittests