Cherry pick `Updating modelopt spec for Mixtral (10660)` into `r2.0.0`
Thanks @ko3n1g, I'll merge that
[🤖]: Hi @janekl 👋,<br><br>we've cherry picked #10660 into `r2.0.0` for you! 🚀<br><br>Please review and approve this cherry pick by your convenience\!