ci(mergify): upgrade configuration to current format (#16)

> [!CAUTION]
> The transformed Mergify configuration is invalid or contains deprecated fields that should have been transformed.
> The `shared` key in your configuration could be the cause, Mergify cannot know what is inside this `shared` key so it cannot modify it.
> In order for the configuration to be valid, you will need to manually modify it.
<hr/>

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.

Do not procrastinate! You **must upgrade** your configuration before **2025-01-31**, otherwise your configuration will stop working.

## 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- `queue_rules → speculative_checks`: The per-queue rule speculative checks has been replaced by a global maximum parallel check in order to improve the performance of test scheduling. (deadline: 2025-01-31)

## 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! 🙌

**Is this update safe to merge?**

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!

**Do I need to do anything special after merging?**

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.

**What if I run into issues or have concerns?**

We're here to help! Feel free to [reach out to our support team](mailto:[email protected]) 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.yml

@@ -17,7 +17,6 @@ shared:
       {{ body }}
     allow_inplace_checks: true
     merge_method: squash
-    speculative_checks: 5
   CheckRuns: &CheckRuns
     - check-success=linters
     - check-success=test
@@ -91,10 +90,9 @@ queue_rules:
       - and:
           - not: *IsPublicHolidays
           - schedule=Mon-Fri 09:00-17:00[Europe/Paris]
-    speculative_checks: 1
     batch_size: 7
     batch_max_wait_time: 5min
-    commit_message_template: null
+    commit_message_template:
     queue_branch_merge_method: fast-forward
     disallow_checks_interruption_from_queues:
       - default
@@ -127,3 +125,6 @@ pull_request_rules:
       request_reviews:
         teams:
           - devs
+
+merge_queue:
+  max_parallel_checks: 5