fix: move dispose_engine import inside lifespan function

The top-level import of dispose_engine from cartsnitch_api.database
caused ImportError at module scope because dispose_engine was not
available when main.py was loaded. The function is only used inside
the lifespan context manager, so move the import there.

Fixes: ImportError cannot import name 'dispose_engine' from 'cartsnitch_api.database'

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitea/workflows/ci.yml

@@ -26,6 +26,7 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12"
+          cache: pip
       - run: pip install ruff
       - name: Ruff lint
         run: ruff check .
@@ -40,6 +41,7 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12"
+          cache: pip
       - name: Install system dependencies
         run: sudo apt-get update && sudo apt-get install -y libpq-dev build-essential
       - run: pip install -e ".[dev]" mypy
@@ -81,13 +83,12 @@ jobs:
       CARTSNITCH_DATABASE_URL: postgresql+asyncpg://cartsnitch:cartsnitch_test@localhost:5432/cartsnitch_test
       CARTSNITCH_REDIS_URL: redis://localhost:6379/0
       CARTSNITCH_JWT_SECRET_KEY: test-secret-do-not-use-in-prod
-      CARTSNITCH_SERVICE_KEY: test-service-key-do-not-use-in-prod
-      CARTSNITCH_FERNET_KEY: wXWQsC0FZlhSz2t_tfVQjNUSP8vgAGG3o3pkjrX8Bw0=
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12"
+          cache: pip
       - name: Install system dependencies
         run: sudo apt-get update && sudo apt-get install -y libpq-dev build-essential
       - run: pip install -e ".[dev]"