Summary:
openpyxl was producing tuples while some older code expects lists. Choosing to convert the tuples to lists (instead of making the other code work with tuples) in case there's other similar issues still out there. Should fix the error mentioned in https://grist.slack.com/archives/C0234CPPXPA/p1652797247167719:
```
Traceback (most recent call last):
File "/gristroot/grist/sandbox/grist/sandbox.py", line 103, in run
ret = self._functions[fname](*args)
File "/gristroot/grist/sandbox/grist/imports/register.py", line 11, in parse_excel
return import_file(file_source)
File "/gristroot/grist/sandbox/grist/imports/import_xls.py", line 20, in import_file
parse_options, tables = parse_file(path)
File "/gristroot/grist/sandbox/grist/imports/import_xls.py", line 26, in parse_file
return parse_open_file(f)
File "/gristroot/grist/sandbox/grist/imports/import_xls.py", line 69, in parse_open_file
table_data_with_types = parse_data.get_table_data(rows, len(headers))
File "/gristroot/grist/sandbox/grist/parse_data.py", line 215, in get_table_data
row.extend([""] * missing_values)
AttributeError: 'tuple' object has no attribute 'extend'
```
Test Plan: Existing tests. Haven't figured out how to reproduce the original error.
Reviewers: georgegevoian
Reviewed By: georgegevoian
Differential Revision: https://phab.getgrist.com/D3434
af1564d410