Fix how status is inferenced in connection_summary

Hi! I am working on mypy in python/mypy#18797

And I've noticed a small thing in your code. Ideally, `SomeEnum.Item.name` should be inferenced as `Literal[NAME_ONE, NAME_TWO, ...]`

But, since you later modify `status` (which is the name of a enum item), it should be explicitly annotated as `str`, not `Literal`.

Author: sobolevn

Diff for: psycopg/psycopg/pq/misc.py

@@ -153,7 +153,7 @@ def connection_summary(pgconn: abc.PGconn) -> str:
     parts = []
     if pgconn.status == OK:
         # Put together the [STATUS]
-        status = TransactionStatus(pgconn.transaction_status).name
+        status: str = TransactionStatus(pgconn.transaction_status).name
         if pgconn.pipeline_status:
             status += f", pipeline={PipelineStatus(pgconn.pipeline_status).name}"