## Issue Addressed
NA
## Proposed Changes
This PR is near-identical to https://github.com/sigp/lighthouse/pull/2652, however it is to be merged into `unstable` instead of `merge-f2f`. Please see that PR for reasoning.
I'm making this duplicate PR to merge to `unstable` in an effort to shrink the diff between `unstable` and `merge-f2f` by doing smaller, lead-up PRs.
## Additional Info
NA
## Proposed Changes
Update to the latest version of the Altair spec, which includes new tests and a tweak to the target sync aggregators.
## Additional Info
This change is _not_ required for the imminent Altair devnet, and is waiting on the merge of #2321 to unstable.
Co-authored-by: Paul Hauner <paul@paulhauner.com>
