ci: drop host port mapping for Mongo service container

The test job failed on the runner with:
  Bind for 0.0.0.0:27017 failed: port is already allocated

because the services.mongo ports: 27017:27017 tries to claim host port
27017, which is occupied (mongod on the runner host). The job container
doesn't need the host mapping — it reaches Mongo over the job's internal
network via the service hostname (MONGODB_URI=mongodb://mongo:27017).
Drop the ports block so the service container schedules cleanly.

This unblocks all PRs, including #6 (Phase A1).

.forgejo/workflows/lint-and-build.yml

@@ -111,8 +111,12 @@ jobs:
         image: mongo:7
         env:
           MONGO_INITDB_DATABASE: normogen_test
-        ports:
+        # No `ports:` mapping: the job container reaches Mongo over the job's
-          - 27017:27017
+        # internal network via the service hostname (MONGODB_URI uses `mongo`,
+        # not localhost). Publishing to a host port is unnecessary and collides
+        # with any mongod already bound to :27017 on the runner host — which
+        # made the service container fail to schedule ("port is already
+        # allocated") and aborted the whole test job before any test ran.
     env:
       MONGODB_URI: mongodb://mongo:27017
       APP_ENVIRONMENT: development