[llvm] [Nomination] Add ST representative to Security group (PR #93176)

[Dimitry Andric via llvm-commits]

https://github.com/DimitryAndric approved this pull request.

ST is STMicroelectronics, who interestingly have the domain `st.com`: https://www.st.com/


https://github.com/llvm/llvm-project/pull/93176