fix: resolve mutex conflicts in Instagram webhook specs (#12154)

This PR fixes flaky test failures in the Instagram webhook specs that
were caused by Redis mutex lock conflicts when
   tests ran in parallel.

 ### The Problem:
The InstagramEventsJob uses a Redis mutex with a key based on sender_id
and ig_account_id to prevent race
conditions. However, all test factories were using the same hardcoded
sender_id: 'Sender-id-1', causing multiple
test instances to compete for the same mutex lock when running in
parallel.

 ### The Solution:
- Updated all Instagram event factories to generate unique sender IDs
using SecureRandom.hex(4)
- Modified test stubs and expectations to work with dynamic sender IDs
instead of hardcoded values
- Ensured each test instance gets its own unique mutex key, eliminating
lock contention

spec/rails_helper.rb

@@ -70,6 +70,7 @@ RSpec.configure do |config|
   config.include SlackStubs
   config.include FileUploadHelpers
   config.include CsvSpecHelpers
+  config.include InstagramSpecHelpers
   config.include Devise::Test::IntegrationHelpers, type: :request
   config.include ActiveSupport::Testing::TimeHelpers
   config.include ActionCable::TestHelper