Change: (magit-todos-exclude-globs) Mark as safe

In one of my projects, I have a `deprecated/` folder with files that had TODOs in them before I deprecated them. I want to the leave the TODOs as-is, but I don't want to be reminded about them in the Magit status buffer. This change allows me to set `magit-todos-exclude-globs` in `.dir-locals.el` without being warned.