ci(mergify): upgrade configuration to current format

[mergify]

Hey there! 👋

We've noticed that your Mergify configuration is using some deprecated fields.
No worries—we've got your back! This automated PR updates your config to align
with the newest standards, ensuring everything keeps running smoothly.

What's Changed?

• queue_rules → speculative_checks: The per-queue rule speculative checks has been replaced by a global maximum parallel check in order to improve the performance of test scheduling.

Why This Matters

Keeping your configuration up-to-date means you'll benefit from the latest
features and improvements Mergify has to offer. Plus, it helps prevent any
unexpected hiccups down the road.

Got Questions? We've Got Answers! 🙌

Q: Is this update safe to merge?

A: Absolutely! We've made sure the changes are compatible with your current
setup. Your workflows should continue to work just as before—if not better!

Q: Do I need to do anything special after merging?

A: Nope! Just merge this PR, and you're all set. If you have any custom
configurations, it's a good idea to give them a quick look to ensure
everything's in order.

Q: What if I run into issues or have concerns?

A: We're here to help! Feel free to reach out to our support
team anytime.

Thanks for being awesome and keeping your configuration up-to-date! If you have
any thoughts or need a hand, don't hesitate to let us know.

Happy merging! 🎉

[mergify]

Merge Protections

Your pull request matches the following merge protections and will not be merged until they are valid.

Changelog requirements

• any of:
  • -title ~= ^feat
  • label = need changelog
  • label = skip changelog

Enforce conventional commit

Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?:

🔎 Reviews

• #changes-requested-reviews-by = 0
• #review-requested = 0
• #review-threads-unresolved = 0