Adds dosfstools to the PKGBUILD depends

[digital-raven]

One of the tools needed by archinstall is mkfs.fatXX and this wasn't automatically installed.

• I don't know if this issue is present on the github. I'll open one if required; the contributing guideline did not impose a requirement for an existing issue.

PR Description:

This adds dosfstools, which provides the mkfs.fat binary which is used in device_handler.py

Tests and Checks

When I run makepkg -s on my system with or without this change, I receive an error that my build did not pass the "validity check". I don't know if this has bearing on the integrity of this change, so I left the following checklist for what I believe would be a good test of this change.

• [ ] Using archinstall as installed using pacman -S archinstall and try to format any partition using a code path that relies on mkfs.fat, archinstall will error because this tool is not installed.
• [ ] When I ran makepkg -si, dosfstools was installed on my system along with archinstall.