Improve FastApi exclusion for Cadwyn incompatibility and link Cadwyn …

[potiuk]

…issue

Cadwyn is not compatible (yet) with FastAPI 0.128.0 - but the changes in FastAPI are deliberately breaking so there is no way we are going to support FastAPI >=0.128.0 unless there is a fix from Cadwyn (and we also need to fix generating models for task-sdk to not use private method that has been removed in FastAPI 0.128.0.

Therefore, it's better to upper-bind FastAPI rather than exclude it, because there might be more versions of FastAPI released before Cadwyn gets fixed.

Also the issue zmievsa/cadwyn#316 has been created, describing the root cause and suggested way how the issue could be fixed in Cadwyn and comment on the reason for upper binding was added to make sure we keep track of it.

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[potiuk]

@jscheffl, @gopidesupavan -> I created the issue in Cadwyn zmievsa/cadwyn#316 , describing the issue and updated the exclusion from #59856 with link to the issue and <= rather than != as this is really something that we will only be able to get rid after Cadwyn releases a new version fixing the compatibility - so it's possible new versions of FastAPI will be released in-between

@pierrejeambrun -> I am not exactly sure about the reasoning of mocking the fastapi._compat.v2.get_long_model_name in our task-sdk/dev/generate_task_sdk_models.py - but since this method is now entirely removed from fastapi, and only Pydantic v2 route is going to be used, it's either not needed, or we'll have to do it differently. It seems it's been a dirty hack from the begginig anyway -> it was added here https://github.com/apache/airflow/pull/58524/changes

[jscheffl]

Thanks for cleaning-up behind my short term fix!

[gopidesupavan]

Thank you @potiuk