In this case data and regex are bytes, so repl argument should be bytes as
well. Before this fix, we would sometimes get this error:
```
calibre, version 7.3.0 (linux, embedded-python: False)
Conversion error: Failed: Convert book 1 of 1 (xxxxxxxxxx)
--- snip ---
2024-03-24 23:43:49 [INFO] Upgrading to EPUB 3...
Traceback (most recent call last):
File "/usr/bin/calibre-parallel", line 21, in <module>
sys.exit(main())
^^^^^^
File "/usr/lib64/calibre/calibre/utils/ipc/worker.py", line 214, in main
result = func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/calibre/calibre/gui2/convert/gui_conversion.py", line 38, in gui_convert_override
gui_convert(input, output, recommendations, notification=notification,
File "/usr/lib64/calibre/calibre/gui2/convert/gui_conversion.py", line 25, in gui_convert
plumber.run()
File "/usr/lib64/calibre/calibre/ebooks/conversion/plumber.py", line 1281, in run
self.output_plugin.convert(self.oeb, self.output, self.input_plugin,
File "calibre_plugins.kepubout.conversion.kepub_output", line 146, in convert
File "/usr/lib64/calibre/calibre/ebooks/conversion/plugins/epub_output.py", line 275, in convert
encryption = self.upgrade_to_epub3(tdir, opf, encryption)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/calibre/calibre/ebooks/conversion/plugins/epub_output.py", line 319, in upgrade_to_epub3
container.commit()
File "/usr/lib64/calibre/calibre/ebooks/oeb/polish/container.py", line 1360, in commit
super().commit(keep_parsed=keep_parsed)
File "/usr/lib64/calibre/calibre/ebooks/oeb/polish/container.py", line 1073, in commit
self.commit_item(name, keep_parsed=keep_parsed)
File "/usr/lib64/calibre/calibre/ebooks/oeb/polish/container.py", line 1017, in commit_item
data = self.serialize_item(name)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/calibre/calibre/ebooks/oeb/polish/container.py", line 1008, in serialize_item
data = re.sub(br'(<[/]{0,1})opf:', r'\1', data)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.12/re/__init__.py", line 186, in sub
return _compile(pattern, flags).sub(repl, string, count)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: sequence item 1: expected str instance, bytes found
```
In my case, the error would show up when converting EPUBs to KEBPUBs.
