include/medialibrary/IDeviceLister.h: Include string

`std::string` is used, but string is not included, causing errors when compiling with mingw-w64
3 jobs for master in 8 minutes and 10 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #393321
amd64 docker
linux

00:08:10

passed #393322
amd64 docker
win32

00:04:03

passed #393323
amd64 docker
win64

00:03:56