device-tree files incorrectly set to audio/vnd.dts

Apparently device tree files are ending with .dts now and that is getting set to an audio-file by shared-mime-info. This caused a problem for us in Builder because we specifically block opening non-text/plain content-types to avoid hitting very bad performance cases in GtkTextView.

https://gitlab.gnome.org/GNOME/gnome-builder/-/issues/1572

Perhaps we need to sniff the first page and look for UTF-8 formatted text?