fix: stop tests from hanging CI (mocha --exit)

Importing the app's modules in tests transitively runs app() (Fastify listen +
scheduler crons), which keeps the Node event loop alive so mocha never exits.
The CI 'Run tests' step therefore hung until the 6h timeout and was cancelled,
so the push-on-production deploy job NEVER ran - no code had deployed for days
(this is why the meteo-alerts fixes appeared to have no effect). Add --exit so
mocha terminates after the run and the pipeline can reach the deploy step.

Author: nicomontanari

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "start": "nodemon src/index.ts",
     "dist": "tsc",
-    "test": "NODE_ENV=test mocha --require ts-node/register --extension ts --spec './tests/**/*.ts'",
+    "test": "NODE_ENV=test mocha --require ts-node/register --extension ts --exit --spec './tests/**/*.ts'",
     "deploy": "docker compose build --no-cache && docker compose up -d --force-recreate"
   },
   "dependencies": {