fix(test): dial the Mongo port the skip-gate actually probes

test_legacy_backups asked conftest's ``mongo_service`` gate about 27018 and
then connected to 27017, so the module only ran where both ports had a
server. CI publishes 27018 only: the gate passed, the connection was
refused, and two tests errored. Every other Mongo test already defaults to
27018.

Masked until now because collection aborted earlier in the run.

Author: AnkushMalaker

backends/advanced/tests/test_legacy_backups.py

@@ -42,7 +42,11 @@
 async def init_db():
     """Beanie refuses to *construct* a Document before initialization, so the two
     mapping tests need a database even though they never write to one."""
-    client = AsyncIOMotorClient(os.getenv("MONGODB_URI", "mongodb://localhost:27017"))
+    # 27018, matching conftest's ``mongo_service`` gate and every other Mongo test.
+    # Dialling 27017 while the gate probes 27018 means the module only runs where
+    # both ports have a server: CI publishes 27018 only, so it skipped the gate and
+    # then failed to connect.
+    client = AsyncIOMotorClient(os.getenv("MONGODB_URI", "mongodb://localhost:27018"))
     name = os.getenv("TEST_DB_NAME", "test_legacy_backups")
     await init_beanie(database=client[name], document_models=[Conversation])
     yield