Use virtualenv for tests

Author: Joonalai

.github/workflows/ci.yml

@@ -17,17 +17,22 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - name: Install dependencies
+      - name: Install venv
         run: |
-          python3 -m pip install -U pip setuptools
-          pip3 install -qr requirements.txt pytest-cov
-          pip3 install -e .
+          apt update
+          apt install -y python3-venv
+      - name: Create virtualenv and install dependencies
+        run: |
+          python3 -m venv --system-site-packages .venv
+          .venv/bin/pip install -U pip setuptools
+          .venv/bin/pip install -qr requirements.txt pytest-cov
+          .venv/bin/pip install -e .
       - name: Run tests
         env:
           QGIS_IN_CI: 1
         run: >
           xvfb-run -s '+extension GLX -screen 0 1024x768x24'
-          python3 -m pytest -v --cov src/pytest_qgis --cov-report=xml -m 'not with_pytest_qt' -p no:pytest-qt tests
+          .venv/bin/pytest -v --cov src/pytest_qgis --cov-report=xml -m 'not with_pytest_qt' -p no:pytest-qt tests
 
       # Upload coverage report. Will not work if the repo is private
       - name: Upload coverage to Codecov