You could disable dynamic shadows for the resupply locker prop entirely. If you want it to still cast shadows, asuming the locker never moves, you could use a blocklight brush for lightmap shadows, which don't have this bug. Alternatively,
info_no_dynamic_shadow can be used to define brush faces you don't want dynamic shadows to be cast upon, which is useful in instances like this where dynamic shadows are bleeding through walls, but this also means expected dynamic shadows, such as player shadows, won't appear. (Although players already don't see their own shadow so its not like those need to be super-realistic anyway.)