DEV: update base url links to respect subfolder installs (#27740)

This change eliminates a couple of instances where subfolder urls are badly formatted, in most cases we can use Discourse.base_url_no_prefix to prevent adding the subfolder to the base url.

spec/helpers/email_helper_spec.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+RSpec.describe EmailHelper do
+  describe "#email_topic_link" do
+    it "respects subfolder" do
+      set_subfolder "/forum"
+      topic = Fabricate(:topic)
+      expect(helper.email_topic_link(topic)).to include("#{Discourse.base_url_no_prefix}/forum/t")
+    end
+  end
+end