load_workbook error in 3.0.5 not in 3.0.4
The attached file cannot be opened by openpyxl 3.0.5, while it works for version 3.0.4
``import openpyxl as oxl``
``oxl.load_workbook('openpyxl.xlsx')``
```
/lib/python3.7/site-packages/openpyxl/descriptors/sequence.py in __set__(self, instance, seq)
23 def __set__(self, instance, seq):
24 if not isinstance(seq, self.seq_types):
---> 25 raise TypeError("Value must be a sequence")
26 seq = [_convert(self.expected_type, value) for value in seq]
27 if self.unique:
TypeError: Value must be a sequence
```
[openpyxl.xlsx](/uploads/4cfba9463b905b7a107b92f97bd20a68/openpyxl.xlsx)
issue