sql/pgwire: portal created before update should not show the updated value

Sent the following pgwire messages to postgres 13.3 and cockroachdb on master (built on c078537681f). The behavior of CRDB is different from Postgres.

```
send
Query {"String": "BEGIN"}
Query {"String": "CREATE TABLE mytable (x int)"}
Query {"String": "INSERT INTO mytable VALUES (1),(2),(3)"}
Parse {"Name": "q3", "Query": "SELECT * FROM mytable"}
Bind {"DestinationPortal": "p3", "PreparedStatement": "q3"}
Query {"String": "UPDATE mytable SET x = 10"}
Execute {"Portal": "p3", "MaxRows": 2}
Sync
----

until
ReadyForQuery
ReadyForQuery
ReadyForQuery
ReadyForQuery
ReadyForQuery
----
```

Postgres:
```
{"Type":"CommandComplete","CommandTag":"BEGIN"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"CommandComplete","CommandTag":"CREATE TABLE"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"CommandComplete","CommandTag":"INSERT 0 3"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"ParseComplete"}
{"Type":"BindComplete"}
{"Type":"CommandComplete","CommandTag":"UPDATE 3"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"DataRow","Values":[{"text":"1"}]}
{"Type":"DataRow","Values":[{"text":"2"}]}
{"Type":"PortalSuspended"}
{"Type":"ReadyForQuery","TxStatus":"T"}
```

CRDB:
```
{"Type":"CommandComplete","CommandTag":"BEGIN"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"CommandComplete","CommandTag":"CREATE TABLE"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"CommandComplete","CommandTag":"INSERT 0 3"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"ParseComplete"}
{"Type":"BindComplete"}
{"Type":"CommandComplete","CommandTag":"UPDATE 3"}
{"Type":"ReadyForQuery","TxStatus":"T"}
{"Type":"DataRow","Values":[{"text":"10"}]}
{"Type":"DataRow","Values":[{"text":"10"}]}
{"Type":"PortalSuspended"}
{"Type":"ReadyForQuery","TxStatus":"T"}
```

So the portal is declared before the row updates, but in cockroach, the portal execution gives value after the updates (i.e. `10`).

Jira issue: CRDB-25086

Epic CRDB-61001