Fix articles being updated every time

[HOGGL]

The pdflatex compiler adds creation date metadata to PDFs. This means the PDF has a different hash even if the source files are left unchanged, leading Git to think they've been updated.

This pull request introduces the smallest change that fixes this but makes the dates meaningless (though I don't know of anything that relies on them).

The files are still compiled each time. A better way to fix this is to cache build artifacts between builds so that only the files that have changed are rebuilt. I can add that if you want but it may lead to issues that mean you have to clear the cache.

Thanks for all the work you do!

[HOGGL]

Before closing in favor of #3 adding how I achieved caching:

  with:
    path: repo

- name: Cache build artifacts
  uses: actions/cache@v5
  with: 
    path: |
      repo/**/*.aux
      repo/**/*.bbl
      repo/**/*.fdb_latexmk
      repo/**/*.out
      repo/**/*.pdf
    key: ${{ github.repository }}

- name: Compile briefs
  uses: xu-cheng/latex-action@v4