'Prepare training data' facing unhashable type error

[Gautam-Rajeev]

Unable to run :

from ragatouille import RAGTrainer
trainer = RAGTrainer(model_name = "MyFineTunedColBERT",
        pretrained_model_name = "colbert-ir/colbertv2.0")

pairs = [
    ("What is the meaning of life ?", "The meaning of life is 42"),
    ("What is Neural Search?", "Neural Search is a terms referring to a family of ")]

trainer.prepare_training_data(raw_data=pairs)

Getting the error :

[<ipython-input-58-5dad2ddb53fa>](https://localhost:8080/#) in <cell line: 1>()
----> 1 trainer.prepare_training_data(raw_data=pairs)

[/usr/local/lib/python3.10/dist-packages/ragatouille/RAGTrainer.py](https://localhost:8080/#) in prepare_training_data(self, raw_data, all_documents, data_out_path, num_new_negatives, hard_negative_minimum_rank, mine_hard_negatives, hard_negative_model_size, pairs_with_labels, positive_label, negative_label)
    123 
    124         self.queries = set([x[0] for x in raw_data])
--> 125         self.collection = list(set(self.collection))
    126         seeded_shuffle(self.collection)
    127 

TypeError: unhashable type: 'Series'

[bclavie]

Thank you for investigating and fixing this! Just had a minor nitpick on the PR that I've changed but all good to me, will be live on PyPi really soon!