MaxOpenConns is not working

[youzhixiaomutou]

Issue description

When I operate MySQL concurrently, the number of actually created connections is greater than the set maximum number of connections. Is my usage wrong? Or is the connection leaked somewhere?

Example code

// fuzz_conn_test.go
func FuzzConn(f *testing.F) {
	db, _ := sql.Open("mysql", "dsn")
	db.SetMaxOpenConns(2)
	db.SetMaxIdleConns(2)
	db.SetConnMaxIdleTime(10 * time.Second)
	db.SetConnMaxLifetime(10 * time.Second)

	f.Fuzz(func(t *testing.T, a int) {
		go func() {
			r, _ := db.Query("select sleep(10)")
			r.Close()
		}()
	})
}

Error log

Configuration

Driver version (or git SHA): v1.8.0

Go version: go version go1.21.8 windows/amd64

Server version: MySQL 5.7+