Validator should not report `ucan/attest` capability in unknown set

[Gozala]

General validation pass only considers passed capability schema, and if capability been parsed does not match it is reported to the validator which includes it in the general error

https://github.com/web3-storage/ucanto/blob/7744f577076dd8f1dde17f37ea6e66472eb39d41/packages/validator/src/capability.js#L740-L742

ucan/attest is only accessed in a specific code path

https://github.com/web3-storage/ucanto/blob/7744f577076dd8f1dde17f37ea6e66472eb39d41/packages/validator/src/lib.js#L578-L594

We should update couple of code paths to exclude ucan/attest from the list of unknown capability reports

https://github.com/web3-storage/ucanto/blob/7744f577076dd8f1dde17f37ea6e66472eb39d41/packages/validator/src/capability.js#L828-L838