feat: test: Add more post-migration sanity checks

[arajasek]

Related Issues

This builds on #11149 to add a few more "vanilla" sanity checks that always apply

Proposed Changes

Check that:

• system actor is now v12
• the Manifest stored in the system actor state matches what Lotus expects

Additional Info

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, build, chore, ci, docs, perf, refactor, revert, style, test
  • area, e.g. api, chain, state, market, mempool, multisig, networking, paych, proving, sealing, wallet, deps
• New features have usage guidelines and / or documentation updates in
  • Lotus Documentation
  • Discussion Tutorials
• Tests exist for new functionality or change in behavior
• CI is green

[snissn]

looks great!

[snissn]

👍

ci failed

[snissn]

Hi! I had approved this pr conditional on the checks passsing, and unfortuantely there's some style checks that are failing here

[arajasek]

Merging, test is failing on base branch too.