MYRNA DOLYNA, Ukraine —In an overgrown minefield, Yulia Boiko kneels down and starts gardening. Years of war have caused weeds to grow high in the abandoned croplands of eastern Ukraine. Clad in flak jacket and face mask, she uses shears to snip back sun-scorched scrub, removing vegetation one careful inch at a time to avoid hidden tripwires. A small patch of earth is eventually exposed.