Fix the following warning when using ebooklib with the latest version of lxml (5.2.1):
ebooklib/epub.py:1423: FutureWarning: This search incorrectly ignores the root element, and will be fixed in a future version. If you rely on the current behaviour, change it to './/xmlns:rootfile[@media-type]'
Fix the following warning when using ebooklib with the latest version of lxml (5.2.1):