Fix gemma3_text tokenizer in mapping

[LysandreJik]

The gemma3_text tokenizer was not in the tokenizer mapping, leading to errors when trying to load text-only models such as google/gemma-3-1b-it

cc @zucchini-nlp @ArthurZucker

To reproduce the error before this PR:

from transformers import pipeline
pipe = pipeline("text-generation", model="google/gemma-3-1b-it")

messages = [
    [
        {
            "role": "system",
            "content": [{"type": "text", "text": "You are a helpful assistant."},]
        },
        {
            "role": "user",
            "content": [{"type": "text", "text": "Write a poem on Hugging Face, the company"},]
        },
    ],
]

output = pipe(messages, max_new_tokens=15)
print(output)

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[ArthurZucker]

Yep thanks

[HuggingFaceDocBuilderDev]

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