use default db port

WebTest/appsettings.json

         }
     },
     "ConnectionStrings": {
-        "default":  "User ID=POSTGRES_USER;Password=POSTGRES_PASSWORD;Host=POSTGRES_HOST;Port=POSTGRES_PORT;Database=POSTGRES_DB;Pooling=true;"
+        "default":  "User ID=POSTGRES_USER;Password=POSTGRES_PASSWORD;Host=POSTGRES_HOST;Port=5432;Database=POSTGRES_DB;Pooling=true;"
     }
 }