Navigation Link: fix regex to allow multiline SVG (#14481)

* Fix regex to check svg. Fixes #14334

* Add tests

app/models/navigation_link.rb

@@ -1,5 +1,5 @@
 class NavigationLink < ApplicationRecord
-  SVG_REGEXP = /<svg .*>/i.freeze
+  SVG_REGEXP = /<svg .*>/im.freeze
 
   before_validation :allow_relative_url, if: :url?
   before_save :strip_local_hostname, if: :url?

spec/models/navigation_link_spec.rb

@@ -13,6 +13,12 @@ RSpec.describe NavigationLink, type: :model do
     it "validates the icon" do
       navigation_link.icon = "test.png"
       expect(navigation_link).not_to be_valid
+      
+      navigation_link.icon = "<svg foo='bar'>"
+      expect(navigation_link).to be_valid
+
+      navigation_link.icon = "<svg foo='bar'\nbaz='lol'\n\n more stuff...\n\n.  >"
+      expect(navigation_link).to be_valid
     end
 
     context "when validating the URL" do