Fixed `lua_run` case sensitivity

[piqey]

Garry's Mod's lua_run entity performs a case sensitive search for the Code KV pair, which was swapped to all-lowercase in HammerAddons' unified FGD.

The currently available lua_run.fgd does not function by default and requires mappers to disable SmartEdit and correct the casing themselves to fix it (Hammer will automatically revert a manually corrected Code KV pair back to the unified FGD's code key upon its activation).

[vrad-exe]

I would add a comment noting as such, make sure someone else doesn't break it again inadvertently