Using `page()` with first-level heading results in an empty page

[talal]

If you insert a page manually using the built-in page function and that page has a first-level heading inside of it then that will result in an empty page which appears before the manually inserted page.

This is because page() always inserts a manual page break and since we also use pagebreak(weak: true) before first-level headings therefore this results in two page breaks which consequently results in an unintended empty page.

To reproduce, use the following snippet:

#page[
= First level heading
#lorem(50)
]