$npm i lodash

//movie.js 수정
import **_uniqBy** from 'lodash/uniqBy'

export default {
...
...
actions {
...
...
		commit('updateState', {
	  movies: **_uniqBy**(Search, 'imdbID'),
  })
...

if(pageLength > 1) {
        for(let page = 2; page <= pageLength; page++) {
          if(page > (number /10)) break
          const res = await axios.get(`https://www.omdbapi.com/?apikey=${OMDB_API_KEY}&s=${title}&type=${type}&y=${year}&page=${page}`)
          const { Search } = res.data
          commit('updateState', {
            movies: [
              ...state.movies,
              ...**_uniqBy**(Search, 'imdbID')]
          })
        }
      }
}