Fix changelog Dangerfile to convert MR IID to a string before comparison

Signed-off-by: Rémy Coutable <remy@rymai.me>

changelogs/unreleased/fix-danger-changelog-bug.yml

+---
+title: Fix changelog Dangerfile to convert MR IID to a string before comparison
+merge_request: 60899
+author:
+type: fixed

danger/changelog/Dangerfile

@@ -38,16 +38,17 @@ end
 def check_changelog_yaml(path)
   raw_file = File.read(path)
   yaml = YAML.safe_load(raw_file)
+  yaml_merge_request = yaml["merge_request"].to_s
 
   fail "`title` should be set, in #{helper.html_link(path)}! #{SEE_DOC}" if yaml["title"].nil?
   fail "`type` should be set, in #{helper.html_link(path)}! #{SEE_DOC}" if yaml["type"].nil?
 
   return if helper.security_mr?
-  return if helper.mr_iid.to_s.empty?
+  return if helper.mr_iid.empty?
 
   cherry_pick_against_stable_branch = helper.cherry_pick_mr? && helper.stable_branch?
 
-  if yaml["merge_request"].nil?
+  if yaml_merge_request.empty?
     mr_line = raw_file.lines.find_index("merge_request:\n")
 
     if mr_line
@@ -55,7 +56,7 @@ def check_changelog_yaml(path)
     else
       message "Consider setting `merge_request` to #{helper.mr_iid} in #{helper.html_link(path)}. #{SEE_DOC}"
     end
-  elsif yaml["merge_request"] != helper.mr_iid && !cherry_pick_against_stable_branch
+  elsif yaml_merge_request != helper.mr_iid && !cherry_pick_against_stable_branch
     fail "Merge request ID was not set to #{helper.mr_iid}! #{SEE_DOC}"
   end
 rescue Psych::Exception