bugfix: don't require category in drafts

[sharmaeklavya2]

Draft articles seemed to unintentionally have 'category' as a required metadata key. I have made them optional, just like non-draft articles.

Background

This is how I found this bug: I recently upgraded pelican, and running pelican on my blog started throwing errors. Here is an excerpt from the traceback:

File "/Users/eklavya/code/repos/web/blog-source/blogVenv/lib/python3.14/site-packages/pelican/generators.py", line 691, in generate_pages
    self.generate_drafts(write)
    ~~~~~~~~~~~~~~~~~~~~^^^^^^^
File "/Users/eklavya/code/repos/web/blog-source/blogVenv/lib/python3.14/site-packages/pelican/generators.py", line 670, in generate_drafts
    category=draft.category,
             ^^^^^^^^^^^^^^
AttributeError: 'Article' object has no attribute 'category'

My articles don't specify categories, and I don't use category subfolders. I use a custom pelican theme that completely ignores categories and uses tags instead.

After making the fix in this pull request, pelican started building my blog again.

Pull Request Checklist

• Ensured tests pass and (if applicable) updated functional test output
• Conformed to code style guidelines by running appropriate linting tools
• Added tests for changed code (I'm not sure whether tests need to be added and where)
• Updated documentation for changed code (no change to documentation required)