Order merged pipelines in get_merged_run (#2452)

Order merged pipelines in get_merged_run

So that the correct one is returned.
I hope this could help with packit/dashboard#417 (comment), but wasn't able to test it locally.
RELEASE NOTES BEGIN
N/A
RELEASE NOTES END

Reviewed-by: Matej Focko

packit_service/models.py

@@ -43,6 +43,7 @@
     null,
     case,
     Table,
+    asc,
 )
 from sqlalchemy.dialects.postgresql import array as psql_array
 from sqlalchemy.ext.declarative import declarative_base
@@ -1571,6 +1572,7 @@ def get_merged_run(cls, first_id: int) -> Optional[Iterable["PipelineModel"]]:
                     else_=PipelineModel.id,
                 ),
             )
+            .order_by(asc("merged_id"))
             .first()
         )