[BUG] Template data validation lost

## 🐛 Bug Report

I have a template Excel file which includes data validations. When I use exceljs to write data to the template the data validations are lost.

Lib version: 3.8.2

## Steps To Reproduce

```javascript
// index.js
const Excel = require("exceljs");
(async () => {
const workbook = new Excel.Workbook();
await workbook.xlsx.readFile("./template.xlsx"); // Has data validation
await workbook.xlsx.writeFile("./output.xlsx"); // Data validation lost
})();
```

See attached sample project: [exceljs-bug.zip](https://github.com/exceljs/exceljs/files/4396512/exceljs-bug.zip)

## The expected behaviour:

Data validation is retained.