Add action to GA4 form event error

- adds a missing attribute for 'action' to the GA4 tracking event on the contact form error message ('error')

app/views/contact/govuk/new.html.erb

@@ -45,6 +45,7 @@
         ga4_auto_tracker_json = {
           event_name: 'form_error',
           type: 'contact',
+          action: 'error',
           text: @errors.values.map { | error_hash | error_hash.first }.join(', '),
           section: ga4_erroring_sections,
           tool_name:  ga4_english_strings[:page_title]

spec/requests/contact_spec.rb

@@ -415,6 +415,7 @@ def response_contains(request, field, expected_value)
     ga4_data = JSON.parse(ga4_auto_element["data-ga4-auto"])
 
     expect(ga4_data["event_name"]).to eq "form_error"
+    expect(ga4_data["action"]).to eq "error"
     expect(ga4_data["type"]).to eq "contact"
     expect(ga4_data["text"]).to eq "The link field cannot be empty, The message field cannot be empty, The email address must be valid, The name field cannot be empty"
     expect(ga4_data["section"]).to eq "What's it to do with?, What are the details?, If you want a reply (optional), If you want a reply (optional)"