Consider narrowing down bare 'except'
Hi, Not really a bug, just something that might save someone some time in the future. I just spent about an hour hunting down a bug in a piece of code because the bare [`except`](https://foss.heptapod.net/openpyxl/openpyxl/-/blob/branch/3.0/openpyxl/descriptors/base.py#L56) in the `_convert()` function in "openpyxl/descriptors/base.py" erroneously caught an `AttributeError` happening somewhere else. I think it would be a good idea to narrow down the `except` there so it doesn't catch any unrelated errors. Thanks!
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