There's a merged pull request on the void-packages repository

mupdf: update to 1.19.1.
https://github.com/void-linux/void-packages/pull/37004

Description:
I also switched from a `tar.gz` tarball to a `tar.xz` one since it's
smaller in size (87 MB vs 62 MB).

#### Testing the changes
- I tested the changes in this PR: **briefly** (I tested the `mupdf` command on a PDF file)