[`MptConfig`] support from pretrained args (#25116)
* support from pretrained args
* draft addition of tests
* update test
* use parrent assert true
* Update src/transformers/models/mpt/configuration_mpt.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>
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Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>
