fix: fix status annotation in connection_summary

Currently enum names are strings, but this is being changed to become
Literal. When this will happen, the type inferred will not be valid
anymore, as we mutate it and manipulate it as string in the function.

See python/mypy#18797

Author: sobolevn

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}"