Use modern uv pip --system call signature

Virtual env environment variable is no longer supported.

.github/workflows/build_docs.yaml

@@ -25,25 +25,21 @@ jobs:
       - name: Install graphviz
         run: sudo apt-get install graphviz
 
-      - name: Set the VIRTUAL_ENV variable for uv to work
-        run: |
-          echo "VIRTUAL_ENV=${Python_ROOT_DIR}" >> $GITHUB_ENV
-
       - name: Update pip/wheel infrastructure and install uv
         run: |
           python -m pip install --upgrade pip
           pip install uv
-          uv pip install wheel
+          uv pip install --system wheel
 
       - name: Install documenteer
-        run: uv pip install 'documenteer[pipelines]==0.8.2'
+        run: uv pip install --system 'documenteer[pipelines]==0.8.2'
 
       - name: Install dependencies
         run: |
-          uv pip install -r requirements.txt
+          uv pip install --system -r requirements.txt
 
       - name: Build and install
-        run: uv pip install --no-deps -v -e .
+        run: uv pip install --system --no-deps -v -e .
 
       - name: Build documentation
         working-directory: ./doc