[BUG] font parameter is being overwritten if used in the same row for different cells

## 🐛 Bug Report

While using exceljs to change the font of diferent cells in the same row, the font is overwritten in both cells to the latest value, and it makes impossible to set font to diferente fields
Lib version: 4.4.0

## Steps To Reproduce

```javascript
for(let i = 17; i < worksheetQuotation._rows.length+1; i++) {
var row = worksheetQuotation.getRow(i);

if(row .getCell(10).value == "TOTAL"){
break;
}

row.getCell(8).font = { name: 'Arial', size: 12, bold: false };
row.getCell(9).font = { name: 'Arial', size: 14, bold: true };
row.commit();
}
If you executed a for like this, the font argument of cell 8 gets the same value as the font argument of cell 9
and the xlsx shows fields in column 9 without bold and fields in column 8 with bold

```

## The expected behaviour:

## Possible solution (optional, but very helpful):

```javascript

```