dual-function-keys: Make left shift KEY_GRAVE

Fixes an issue where ` wouldn't work in neovim due to the escape key
being recognized as pressed.

modules/dual-function-keys.nix

@@ -31,8 +31,8 @@
         - KEY: KEY_RIGHTSHIFT
           TAP: [ KEY_LEFTMETA, KEY_F2 ]
           HOLD: KEY_RIGHTSHIFT
-        - KEY: KEY_ESC
+        - KEY: KEY_LEFTSHIFT
           TAP: KEY_GRAVE
-          HOLD: KEY_ESC
+          HOLD: KEY_LEFTSHIFT
   '';
 }