chore(deps): update dependency geoalchemy2 to v0.18.0

Author: renovate-bot

samples/snippets/requirements.txt

@@ -2,7 +2,7 @@ alembic===1.14.0; python_version == '3.8'
 alembic==1.16.4;  python_version >= '3.9'
 certifi==2025.7.14
 charset-normalizer==3.4.2
-geoalchemy2==0.17.1
+geoalchemy2==0.18.0
 google-api-core[grpc]==2.25.1
 google-auth==2.40.3
 google-cloud-bigquery===3.30.0; python_version == '3.8'