Improve CI workflow for backend tests by enhancing virtual environment setup

- Added a function to install the python3-venv package if the virtual environment creation fails due to missing ensurepip.
- Improved error handling and messaging for the installation process, ensuring compatibility with both root and non-root users.
- Streamlined the activation of the virtual environment for better clarity in the CI pipeline.

.gitea/workflows/build.yml

@@ -27,6 +27,8 @@ jobs:
 
       # No usamos actions/setup-python: en runners self-hosted (Debian) suele fallar
       # al descargar versiones desde el manifest. Se usa python3 del sistema + venv.
+      # En Debian/Ubuntu hace falta el paquete python3-venv (ensurepip); si falla el venv,
+      # se intenta instalar con apt (root en act/containers, sudo en servidor típico).
       - name: Instalar dependencias y ejecutar tests del backend
         env:
           TEST_DATABASE_URL: ${{ secrets.TEST_DATABASE_URL }}
@@ -38,11 +40,27 @@ jobs:
             exit 1
           fi
           python3 --version
-          if ! python3 -m venv "$GITHUB_WORKSPACE/.pytest-venv" 2>/dev/null; then
-            echo "python3 -m venv falló. En Debian/Ubuntu instala: sudo apt-get install -y python3-venv"
-            exit 1
+          VENV="$GITHUB_WORKSPACE/.pytest-venv"
+          install_python3_venv() {
+            export DEBIAN_FRONTEND=noninteractive
+            if ! command -v apt-get >/dev/null 2>&1; then
+              echo "::error::No hay apt-get. Instala manualmente el paquete equivalente a python3-venv."
+              return 1
+            fi
+            if [ "$(id -u)" -eq 0 ]; then
+              apt-get update -qq
+              apt-get install -y python3-venv
+            else
+              sudo apt-get update -qq
+              sudo apt-get install -y python3-venv
+            fi
+          }
+          if ! python3 -m venv "$VENV" 2>/dev/null; then
+            echo "venv falló (ensurepip no disponible). Instalando python3-venv..."
+            install_python3_venv
+            python3 -m venv "$VENV"
           fi
-          . "$GITHUB_WORKSPACE/.pytest-venv/bin/activate"
+          . "$VENV/bin/activate"
           python -m pip install --upgrade pip
           pip install -r "$GITHUB_WORKSPACE/backend/requirements.txt"
           cd "$GITHUB_WORKSPACE/backend"