chore(ci): bump prague to stable and osaka to develop

[spencer-tb]

🗒️ Description

Bumps Prague to stable and Osaka to develop in our CI.

I think we should create an initial Osaka release after merging this where fixtures_stable would contain Prague and fixtures_develop up to Osaka (refill-ing all our existing tests).

I added a temp EELS branch so we can refill all of our tests for Osaka:

• https://github.com/spencer-tb/execution-specs/tree/forks/osaka

Note that branch is based off:

• https://github.com/marioevz/execution-specs/tree/forks/prague

So we should probably proceed with #1454 first, then update our temp osaka branch.

🔗 Related Issues

Requires #1507 and #1454.

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.

[marioevz]

Actually requires #1508 if we want to wait for the last Prague-as-develop release.