Ensure that `GetCellFormula` returns the complete path for cell formulas, including the file path.
**Description** I have a sheet where I put `='C:\Users\Alex\Sheet1'!$A$3` as formula into a cell. When I am calling `GetCellFormula` on that cell I don't get the whole path. I get `[1]Sheet1!$A$3`. **Steps to reproduce the issue:** 1. Create excel file with such formula 2. Process it with excelize 3. Call GetCellFormula on the cell **Describe the results you received:** `[1]Sheet1!$A$3` **Describe the results you expected:** `='C:\Users\Alex\Sheet1'!$A$3` (or without the `=`) **Output of `go version`:** go version go1.21.3 windows/amd64 **Excelize version or commit ID:** v2.8.1 **Environment details (OS, Microsoft Excel™ version, physical, etc.):** Windows 10, Excel from Office 365