switch to uv for pip installs

Author: hjwp

.github/workflows/tests.yml

@@ -68,11 +68,12 @@ jobs:
             tree \
             locales
           sudo locale-gen en_GB.UTF-8
+          pip install uv
 
       - name: Install Python requirements.txt globally
         shell: bash
         run: |
-          pip install .
+          uv pip install --system  .
 
       - name: Install Python requirements.txt into virtualenv
         shell: bash