fix Enums toUtf8Bytes errors

[lhaox]

What this PR does / why we need it?

一个对象中如果有属性是枚举类型，且枚举值为中文命名，对其进行toJSONBytes序列化时，并不能得到期望的值。测试代码如下所示：

@Test
public void testEnum() {
     Bean bean = new Bean();
     bean.setTestEnum(TestEnum.第二);
     bean.setName("zhangsan");
     byte[] bytes = JSON.toJSONBytes(bean, JSONWriter.Feature.WriteEnumsUsingName);
     System.out.println(new String(bytes, StandardCharsets.UTF_8));
}

@Data
static class Bean {
    private TestEnum testEnum;
    private String name;
}

@SuppressWarnings("all")
enum TestEnum {
    第一,
    第二,
}

期望的结果：{"name":"zhangsan","testEnum":"第二"}
实际的结果：{"name":"zhangsan","testEnum":",�"}

经排查，com.alibaba.fastjson2.writer.FieldWriterEnum中使用了过时的getBytes方法复制bytes导致，此方法并不能真正意义上的对字节数组进行复制

Summary of your change

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

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