make self-hosted runner install into a venv

.github/workflows/run_tests.yml

@@ -8,9 +8,11 @@ jobs:
 
       - name: Install Manta from Source
         run: |
-          ls -lah
-          pwd
-          pip freeze
+          # Make venv
+          python3 -m venv venv/
+          source venv/bin/activate
+
+          # Update pip
           python3 -m pip install -U pip
 
           # omitting the following commmand causes the version of setuptools
@@ -20,6 +22,7 @@ jobs:
           # https://github.com/pypa/setuptools/issues/3269#issuecomment-1254507377
           export DEB_PYTHON_INSTALL_LAYOUT=deb_system
 
+          # Install Manta, with optional dev-only dependencies
           python -m pip install ".[dev]"
 
       - name: Run tests