should not autofit a column with merged cells

Steps to Reproduce

1. imported the attached file in KEIKAI-513
2. double click column D with a merged cell

Current Result

enlarge the column width

Expected Result

doesn't change the column width

Debug Information

• Excel resizes column D, E, F based on the text width of those non-merged cells in the column.
• google sheets enlarges width each time:
  
• According to https://support.microsoft.com/en-us/topic/you-cannot-use-the-autofit-feature-for-rows-or-columns-that-contain-merged-cells-in-excel-34b54dd7-9bfc-6c8f-5ee3-2715d7db4353
  it looks like it's by design.