ci(mergify): strip merge commit HTML comments (#9499)

Tell Mergify to remove noisy HTML comments in the PR description from
the Git merge commit.

As per the NOTE in [Mergify Template
docs](https://docs.mergify.com/configuration/data-types/#template):
> By default, the HTML comments are stripped from `body`. To get the
full body, you can use the `body_raw` attribute.

.github/PULL_REQUEST_TEMPLATE.md

@@ -8,33 +8,19 @@ closes: #XXXX
 refs: #XXXX
 
 ## Description
-
-<!-- Add a description of the changes that this PR introduces and the files that
-are the most critical to review.
--->
+<!-- Add a description of the changes that this PR introduces and the files that are the most critical to review. -->
 
 ### Security Considerations
-
-<!-- Does this change introduce new assumptions or dependencies that, if violated, could introduce security vulnerabilities? How does this PR change the boundaries between mutually-suspicious components? What new authorities are introduced by this change, perhaps by new API calls? 
--->
+<!-- Does this change introduce new assumptions or dependencies that, if violated, could introduce security vulnerabilities? How does this PR change the boundaries between mutually-suspicious components? What new authorities are introduced by this change, perhaps by new API calls? -->
 
 ### Scaling Considerations
-
 <!-- Does this change require or encourage significant increase in consumption of CPU cycles, RAM, on-chain storage, message exchanges, or other scarce resources? If so, can that be prevented or mitigated? -->
 
 ### Documentation Considerations
-
-<!-- Give our docs folks some hints about what needs to be described to downstream users.
-
-Backwards compatibility: what happens to existing data or deployments when this code is shipped? Do we need to instruct users to do something to upgrade their saved data? If there is no upgrade path possible, how bad will that be for users?
-
--->
+<!-- Give our docs folks some hints about what needs to be described to downstream users.  Backwards compatibility: what happens to existing data or deployments when this code is shipped? Do we need to instruct users to do something to upgrade their saved data? If there is no upgrade path possible, how bad will that be for users? -->
 
 ### Testing Considerations
-
-<!-- Every PR should of course come with tests of its own functionality. What additional tests are still needed beyond those unit tests? How does this affect CI, other test automation, or the testnet?
--->
+<!-- Every PR should of course come with tests of its own functionality. What additional tests are still needed beyond those unit tests? How does this affect CI, other test automation, or the testnet? -->
 
 ### Upgrade Considerations
-
 <!-- What aspects of this PR are relevant to upgrading live production systems, and how should they be addressed? -->

.mergify.yml

@@ -1,7 +1,11 @@
 # Linear queue for the main branch.
 queue_rules:
   - name: main
-    conditions:
+    commit_message_template: |-
+      {{ title }} (#{{ number }})
+
+      {{ body | trim }}
+    queue_conditions:
       - base=master
       # Require integration tests before merging only
       - or:
@@ -30,7 +34,7 @@ pull_request_rules:
     actions:
       queue:
         name: main
-        method: merge
+        merge_method: merge
   - name: rebase updates then merge to master
     conditions:
       - base=master
@@ -49,7 +53,7 @@ pull_request_rules:
     actions:
       queue:
         name: main
-        method: merge
+        merge_method: merge
         update_method: rebase
   - name: squash to master
     conditions:
@@ -69,4 +73,4 @@ pull_request_rules:
     actions:
       queue:
         name: main
-        method: squash
+        merge_method: squash