Merge instead of squash Scala Steward PRs

Author: fthomas

.mergify.yml

@@ -25,4 +25,4 @@ pull_request_rules:
   - status-success=Build and Test (ubuntu-latest, 2.13, temurin@11)
   actions:
     merge:
-      method: squash
+      method: merge

build.sbt

@@ -78,7 +78,7 @@ ThisBuild / mergifyPrRules := {
     MergifyPrRule(
       "merge scala-steward's PRs",
       List(authorCondition) ++ mergifySuccessConditions.value,
-      List(MergifyAction.Merge(Some("squash")))
+      List(MergifyAction.Merge(Some("merge")))
     )
   )
 }