fs_mgr: IWYU include <algorithm> for std::sort

GCC 14 starts to no longer include <algorithm> by default, resulting in
it needing to be explicitly declared.

Test: Recompiled with GCC 14 and succeeded

Change-Id: Ifc5dd58b7476ba728ae604cd2924cb68fbcab701
Signed-off-by: Christopher Fore <csfore@posteo.net>