`use_nix` attempts to pass argument to `--extra-deprecated-features` as a file to `nix`

``` use_nix --arg avr false --extra-deprecated-features url-literals ``` ``` ... +++ _nix print-dev-env --profile /Users/atemu/qmk_firmware/.direnv/nix-tmp-profile.1083077 --impure --arg avr false --extra-deprecated-features --file url-literals +++ /run/current-system/sw/bin/nix --no-warn-dirty --extra-experimental-features 'nix-command flakes' print-dev-env --profile /Users/atemu/qmk_firmware/.direnv/nix-tmp-profile.1083077 --impure --arg avr false --extra-deprecated-features --file url-literals warning: unknown deprecated feature '--file' error: '--arg' and '--argstr' are incompatible with flakes Try '/run/current-system/sw/bin/nix --help' for more information. ... ``` Trying to work around this by explicitly passing the file produces: ``` +++ _nix print-dev-env --profile /Users/atemu/qmk_firmware/.direnv/nix-tmp-profile.1083681 --impure --arg avr false --extra-deprecated-features --file . +++ /run/current-system/sw/bin/nix --no-warn-dirty --extra-experimental-features 'nix-command flakes' print-dev-env --profile /Users/atemu/qmk_firmware/.direnv/nix-tmp-profile.1083681 --impure --arg avr false --extra-deprecated-features --file shell.nix ``` It just eats the arg‽