Fixes No such file or directory for pager_duty/validator

https://gitlab.com/gitlab-org/gitlab/-/issues/322901

Fixes:
No such file or directory lib/pager_duty/validator/schemas/message.json

changelogs/unreleased/322901-fix-pagerduty-webhook.yml

+---
+title: 'Fixes: No such file or directory lib/pager_duty/validator/schemas/message.json'
+merge_request: 55725
+author:
+type: fixed

lib/pager_duty/webhook_payload_parser.rb

@@ -2,7 +2,7 @@
 
 module PagerDuty
   class WebhookPayloadParser
-    SCHEMA_PATH = File.join('lib', 'pager_duty', 'validator', 'schemas', 'message.json')
+    SCHEMA_PATH = Rails.root.join('lib', 'pager_duty', 'validator', 'schemas', 'message.json')
 
     def initialize(payload)
       @payload = payload
@@ -66,7 +66,7 @@ module PagerDuty
     end
 
     def valid_message?(message)
-      ::JSONSchemer.schema(Pathname.new(SCHEMA_PATH)).valid?(message)
+      ::JSONSchemer.schema(SCHEMA_PATH).valid?(message)
     end
   end
 end

spec/lib/pager_duty/webhook_payload_parser_spec.rb

 # frozen_string_literal: true
 
-require 'fast_spec_helper'
-require 'json_schemer'
+require 'spec_helper'
 
 RSpec.describe PagerDuty::WebhookPayloadParser do
   describe '.call' do