Pass formats explicitly when rendering .md file

Changelog: other
EE: true

ee/app/services/merge_requests/create_from_vulnerability_data_service.rb

@@ -68,6 +68,7 @@ module MergeRequests
       # This currently applies only the first diff
       render_template(
         file: 'vulnerabilities/remediation',
+        formats: :patch,
         locals: {
           diff: diffs.first,
           head_commit: head_commit,
@@ -80,12 +81,13 @@ module MergeRequests
     def render_description(vulnerability)
       render_template(
         file: 'vulnerabilities/merge_request_description',
+        formats: :md,
         locals: { vulnerability: vulnerability }
       )
     end
 
-    def render_template(file:, locals:)
-      ActionController::Base.new.render_to_string(template: file, locals: locals)
+    def render_template(file:, locals:, formats:)
+      ApplicationController.render(template: file, locals: locals, formats: formats)
     end
 
     def can_create_merge_request?(source_branch)