pgx5 connection CopyFrom failing for JSON field where value is string

Hello,
I am trying to using CopyFrom with pgx5 connection to copy from a table with a JSON field but the json is inserted in the original insert query as '"json_string"'. When using CopyFrom with rows pgx5.Rows and a JSON value of this string, it throws an error:
ERROR: invalid input syntax for type json (SQLSTATE 22P02)

Steps to reproduce the behavior:

```
package main

import (
"context"
"fmt"
"github.com/golang/glog"
"github.com/jackc/pgx/v5"
"log"
"os"
"strings"
)

func main() {
var err error

conn, err := pgx.Connect(context.Background(), os.Getenv("SOURCE_DATABASE_URL"))
if err != nil {
glog.Errorln("Error connecting to db: %v", err)
}
defer conn.Close(context.Background())

_, err = conn.Exec(context.Background(), "CREATE TABLE testtable (id SERIAL PRIMARY KEY, json_column JSON)")
if err != nil {
glog.Errorln("Error creating table: %v", err)
}

_, err = conn.Exec(context.Background(), `INSERT INTO testtable (json_column) VALUES ('"json_string"')`)
if err != nil {
glog.Errorln("Error inserting data: %v", err)
}

if rows, err = conn.Query(context.Background(), "SELECT * FROM testtable"); err != nil {
glog.Errorf("Error querying data from testtable: %v", err)
}
defer rows.Close()

noOfColumns := len(rows.FieldDescriptions())

columns := make([]string, noOfColumns)
for i, col := range rows.FieldDescriptions() {
columns[i] = string(col.Name)
}

table := "public.testtable"

schemaTable := strings.SplitN(table, ".", 2)

connTarget, _ := pgx.Connect(context.Background(), os.Getenv("TARGET_DATABASE_URL"))
defer connTarget.Close(context.Background())

_, err = connTarget.Exec(context.Background(), "CREATE TABLE testtable (id SERIAL PRIMARY KEY, json_column
JSON)")
if err != nil {
glog.Errorln("Error creating table: %v", err)
}

if _, err = connTarget.CopyFrom(context.Background(), schemaTable, columns, rows); err != nil {
glog.Errorln("Error executing COPY SQL for table", err)
}
}
```

**Version**
- Go: go version go1.21.3 darwin/arm64
- PostgreSQL: PostgreSQL 15.5 (Homebrew) on aarch64-apple-darwin23.2.0, compiled by Apple clang version 15.0.0 (clang-1500.1.0.2.5), 64-bit
- pgx: github.com/jackc/pgx/v5 v5.5.0

**Edited code: 1/03/24

Start by running the supplied Go reproduction against PostgreSQL and tracing connTarget.CopyFrom with the pgx.Rows source. Done would be a maintainer-confirmed explanation or fix for the JSON string failure, with regression coverage if appropriate.

Written by the indexing model from the issue text.