6689a385d1
This fixes a harmless error from systemd-udevd that looks like: Dec 23 15:35:23 dellbook systemd-udevd[696]: /nix/store/iixya3ni5whybpq9zz1h7f4pyw7nhd19-udev-rules/99-local.rules:25 Invalid value "..." for RUN (char 101: invalid substitution type), ignoring, but please fix it. Using $$ fixes it using the escaping documented at https://www.freedesktop.org/software/systemd/man/udev.html.
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