Fix Ruby 2.7 warnings for MergeabilityCheckService

In Ruby 3.0, positional arguments and keyword arguments will be
separated. In Ruby 2.7, deprecation warnings related to keyword
arguments show up.

Explicitly specify passing keyword arguments instead of a Hash
object by using double splat operator.

app/services/merge_requests/mergeability_check_service.rb

@@ -88,7 +88,7 @@ module MergeRequests
         sleep_sec: retry_lease ? 1.second : 0
       }
 
-      in_lock(lease_key, lease_opts, &block)
+      in_lock(lease_key, **lease_opts, &block)
     end
 
     def payload