After a quick search, I found similar case ( https://community.openstreetmap.org/t/abandoned-railway-that-is-now-a-foot-way/97349/6 ) which suggests to tag it similarly to this ( https://www.openstreetmap.org/way/345255641 ). Just notice that these tracks are abandoned but still very likely to be reused again (railway company still has plans for the route Corinth-Kalamata).