Fix incorrect MR popovers

Fixes a bug where cross-project MR references were showing incorrect
popovers

lib/banzai/filter/references/merge_request_reference_filter.rb

@@ -58,7 +58,7 @@ module Banzai
         end
 
         def data_attributes_for(text, parent, object, **data)
-          super.merge(project_path: current_parent_path, iid: object.iid, mr_title: object.title)
+          super.merge(project_path: parent.full_path, iid: object.iid, mr_title: object.title)
         end
 
         private

lib/gitlab/markdown_cache.rb

@@ -3,7 +3,7 @@
 module Gitlab
   module MarkdownCache
     # Increment this number every time the renderer changes its output
-    CACHE_COMMONMARK_VERSION        = 27
+    CACHE_COMMONMARK_VERSION        = 28
     CACHE_COMMONMARK_VERSION_START  = 10
 
     BaseError = Class.new(StandardError)

spec/lib/banzai/filter/references/merge_request_reference_filter_spec.rb

@@ -142,6 +142,17 @@ RSpec.describe Banzai::Filter::References::MergeRequestReferenceFilter do
       expect(doc.text).to eq("Merge (#{reference}.)")
     end
 
+    it 'has correct data attributes' do
+      doc = reference_filter("Merge (#{reference}.)")
+
+      link = doc.css('a').first
+
+      expect(link.attr('data-project')).to eq project2.id.to_s
+      expect(link.attr('data-project-path')).to eq project2.full_path
+      expect(link.attr('data-iid')).to eq merge.iid.to_s
+      expect(link.attr('data-mr-title')).to eq merge.title
+    end
+
     it 'ignores invalid merge IDs on the referenced project' do
       exp = act = "Merge #{invalidate_reference(reference)}"