fd leak when using read_only mode
*Created originally on Bitbucket by [wangqr](https://bitbucket.org/%7B958821c4-224d-41d6-a610-a777368ffca2%7D/)*
I’m using the read-only example [here](https://openpyxl.readthedocs.io/en/stable/optimized.html#read-only-mode). I found that the file is not properly closed after reading the content. After reading the source, I guess [maybe it is for the lazy loading](https://bitbucket.org/openpyxl/openpyxl/src/3278d1313e670e456aa5de7f0a15b858660e406c/openpyxl/reader/excel.py#lines-282).
Is there a proper way to close the file after reading when using the read-only mode, other than deleting `ws`, `wb` and force a garbage collection?
issue