Fixes milestone issuable assignee URL

Closes #33124

app/views/shared/milestones/_issuable.html.haml

@@ -26,6 +26,6 @@
 
     %span.assignee-icon
       - assignees.each do |assignee|
-        = link_to polymorphic_path(base_url_args, { milestone_title: @milestone.title, assignee_id: assignee.id, state: 'all' }),
+        = link_to polymorphic_path(issuable_type_args, { milestone_title: @milestone.title, assignee_id: assignee.id, state: 'all' }),
                   class: 'has-tooltip', title: "Assigned to #{assignee.name}", data: { container: 'body' } do
           - image_tag(avatar_icon(assignee, 16), class: "avatar s16", alt: '')

changelogs/unreleased/milestone-avatar-issuable-link.yml

+---
+title: Fixed milestone issuable assignee link URL
+merge_request:
+author:
+type: fixed

spec/views/shared/milestones/_issuable.html.haml.rb

+require 'spec_helper'
+
+describe 'shared/milestones/_issuable.html.haml' do
+  let(:project) { create(:project) }
+  let(:user) { create(:user) }
+  let(:milestone) { create(:milestone, project: project) }
+  let(:issuable) { create(:issue, project: project, assignees: [user]) }
+
+  before do
+    assign(:project, project)
+    assign(:milestone, milestone)
+  end
+
+  it 'avatar links to issues page' do
+    render 'shared/milestones/issuable', issuable: issuable, show_project_name: true
+
+    expect(rendered).to have_css("a[href='#{project_issues_path(project, milestone_title: milestone.title, assignee_id: user.id, state: 'all')}']")
+  end
+end