Update CI workflow to include database migration before running tests

- Added an environment variable for the test database URL and executed an Alembic migration to ensure the database schema is up-to-date prior to running tests.
- This change aims to improve the reliability of test execution by ensuring the correct database state.

.gitea/workflows/build.yml

@@ -64,6 +64,8 @@ jobs:
           python -m pip install --upgrade pip
           pip install -r "$GITHUB_WORKSPACE/backend/requirements.txt"
           cd "$GITHUB_WORKSPACE/backend"
+          export DATABASE_URL="$TEST_DATABASE_URL"
+          alembic upgrade head
           pytest -q tests -v -ra -s
 
   build: