Reorder items in transaction.active_record docs

The `transaction.active_record` event is about transactions. Let's
first document the transaction object, then the transaction state,
and finally the connection in case you need more context.

guides/source/active_support_instrumentation.md

@@ -412,9 +412,9 @@ This event is emmited for every transaction to the database.
 
 | Key | Value |
 | -------------------- | ---------------------------------------------------- |
-| `:connection` | Connection object |
-| `:transaction` | Transaction object
+| `:transaction` | Transaction object |
 | `:outcome` | `:commit`, `:rollback`, `:restart`, or `:incomplete` |
+| `:connection` | Connection object |
 
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