Right align in sample invoice

In the [sample invoice](https://weasyprint.org/samples/invoice/invoice.pdf) the invoice number doesn't correctly align to the right, like the rest of the content. This seems to be related to the PDF rendering by weasyprint, because the source HTML + CSS renders the text correctly.

Start with the sample invoice PDF and compare it with the linked source HTML and CSS, focusing on the invoice number's right alignment. Trace the WeasyPrint PDF-rendering path involved in that content and verify completion by producing a PDF in which the invoice number aligns with the other right-aligned content.

Written by the indexing model from the issue text.