chore(backend): update test execution strategy in Dockerfile

Update Jest test runner configuration to use `--runInBand` flag in Docker build process for more reliable test execution in containerized environment.

backend/Dockerfile

@@ -17,7 +17,7 @@ COPY prisma ./prisma
 COPY src ./src
 COPY tsconfig.json nest-cli.json ./
 RUN ./node_modules/.bin/prisma generate
-RUN npm test
+RUN npm test -- --runInBand
 RUN npm run build
 
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