Test the success message on the clean path

Assert the action emits its "No incompatible placeholder changes" success
message when nothing changed. Captures `UI.success` (the lane runner emits its
own "Driving the lane" message too) and checks ours is among them, so it stays
robust to the runner's output. Verified it bites: removing the
`report(violations)` call fails this example.

Author: jkmassel

spec/ios_lint_localization_placeholder_changes_spec.rb

@@ -37,6 +37,17 @@ def lint_placeholder_changes(old:, new:, **extra_params)
     expect(result).to eq([])
   end
 
+  it 'prints a success message when there are no incompatible changes' do
+    # The lane runner also emits `UI.success` ("Driving the lane …"), so capture all of them and
+    # assert ours is among them rather than constraining every call.
+    messages = []
+    allow(FastlaneCore::UI).to receive(:success) { |m| messages << m }
+
+    lint_placeholder_changes(old: '"greeting" = "Hi %@";', new: '"greeting" = "Hello %@";')
+
+    expect(messages.join("\n")).to include('No incompatible placeholder changes')
+  end
+
   it 'reports and aborts when an existing key changes its placeholder type' do
     expect(FastlaneCore::UI).to receive(:abort_with_message!)