Sahih International translation of [29:46]:
And do not argue with the People of the Scripture except in a way that is best, except for those who commit injustice among them, and say, "We believe in that which has been revealed to us and revealed to you. And our God and your God is one; and we are Muslims [in submission] to Him."
Word used here is ظَلَمُوا۟. Another word with same root is used in another place in a way similar to "those who sin have commited injustice to themselves".
Therefore not believing in Qur'an is unjust meaning there can be no just person of book/scripture.
Is the injustice in 29:46 a specific form? is there any tafseer on this?
Remember that prefix "al-" is not used in 29:46. The prefix "al-" means "The" for example "al-Malik" means "The King" .