Fix display of IP addresses in audit logs

The `ip_address` column returns an IPAddr, which doesn't specify a JSON
representation so we get the Rails default of a hash of its instance
variables. We need an explicit `to_s` to show it in human-readable form.

ee/app/presenters/audit_event_presenter.rb

@@ -18,7 +18,7 @@ class AuditEventPresenter < Gitlab::View::Presenter::Simple
   end
 
   def ip_address
-    audit_event.ip_address || details[:ip_address]
+    audit_event.ip_address&.to_s || details[:ip_address]
   end
 
   def details

ee/changelogs/unreleased/fix-audit-event-ip-address-display.yml

+---
+title: Fix display of IP addresses in audit logs
+merge_request: 35356
+author:
+type: fixed

ee/spec/presenters/audit_event_presenter_spec.rb

@@ -107,6 +107,10 @@ RSpec.describe AuditEventPresenter do
       expect(presenter.ip_address).to eq('10.2.1.1')
     end
 
+    it 'survives a round trip from JSON' do
+      expect(Gitlab::Json.parse(presenter.ip_address.to_json)).to eq(presenter.ip_address)
+    end
+
     it 'falls back to the details hash' do
       audit_event.update(ip_address:  nil)