[tests] add tests for flux modular (t2i, i2i, kontext) (#12566)
* start flux modular tests.
* up
* add kontext
* up
* up
* up
* Update src/diffusers/modular_pipelines/flux/denoise.py
Co-authored-by: YiYi Xu <yixu310@gmail.com>
* up
* up
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Co-authored-by: YiYi Xu <yixu310@gmail.com>