Modify backend/.Dockerfile to copy /tests

Author: YuriiMotov

backend/Dockerfile

@@ -34,6 +34,7 @@ COPY ./scripts /app/scripts
 COPY ./pyproject.toml ./uv.lock ./alembic.ini /app/
 
 COPY ./app /app/app
+COPY ./tests /app/tests
 
 # Sync the project
 # Ref: https://docs.astral.sh/uv/guides/integration/docker/#intermediate-layers