[DOC] Fix typo in creating-pdf-documents.md (#1118)

- Mulit-Article renamed to Multi-Article

docs/creating-pdf-documents.md

@@ -213,7 +213,7 @@ If you have a block or notebook cell that you do now want to render to your LaTe
 
 (multi-article-exports)=
 
-## Mulit-Article Exports
+## Multi-Article Exports
 
 Sometimes you may want to combine multiple MyST documents into a single export, for example a thesis or a book. MyST makes this possible with multi-article exports for PDFs built with either $\LaTeX$ or Typst.