[Gui] Preferences - Change macro path selection from File to Folder

[Syres916]

Thank you for creating a pull request to contribute to FreeCAD! To ease integration, we ask you to conform to the following items. Pull requests which don't satisfy all the items below might be rejected. If you are in doubt with any of the items below, don't hesitate to ask for help in the FreeCAD forum!

• Your pull request is confined strictly to a single module. That is, all the files changed by your pull request are either in App, Base, Gui or one of the Mod subfolders. If you need to make changes in several locations, make several pull requests and wait for the first one to be merged before submitting the next ones
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[donovaly]

Thanks!