Fix CohereEmbeddingOperator input_text normalization before rendering

[MannXo]

Move the single-string normalization of input_text from __init__ into execute().

input_text is a template field, so it is rendered after the constructor runs. Wrapping a plain string into a list in __init__ acts on the un-rendered Jinja expression, so a templated input_text (for example one that resolves to a list under native rendering) is normalized before it is ever rendered. Doing it in execute() operates on the rendered value.

Part of the template-field constructor burn-down; removes the CohereEmbeddingOperator entry from scripts/ci/prek/validate_operators_init_exemptions.txt in the same PR, as the hook requires.

related: #70296

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Was generative AI tooling used to co-author this PR?

• Yes — Claude Code (Opus 4.8)

Generated-by: Claude Code (Opus 4.8) following the guidelines

[boring-cyborg]

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[shahar1]

Well done!
For next times - please ask your LLM to reduce amount of comments (the top comment in execute isn't necessary).
I resolved a conflict with the text file.

[boring-cyborg]

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