add SUF-CMA claim in META.yml

[rtjk]

This pull request simply adds claimed-security: SUF-CMA to META.yml, as declared in FIPS 204:

ML-DSA is designed to be strongly existentially unforgeable under chosen message attack (SUF-CMA).
That is, it is expected that even if an adversary can get the honest party to sign arbitrary messages, the
adversary cannot create any additional valid signatures based on the signer’s public key, including on
messages for which the signer has already provided a signature.

The purpose is to allow liboqs to test this property after importing ML-DSA.