Mark test as flaky

This test occasionally fails on CI with

```
Selenium::WebDriver::Error::UnknownError:
       unknown error: unhandled inspector error: {"code":-32000,"message":"Node with given id does not belong to the document"}
```

spec/features/timeout_spec.rb

@@ -1,6 +1,6 @@
 require "rails_helper"
 
-RSpec.feature "Teacher Student Loan Repayments claims", js: true do
+RSpec.feature "Teacher Student Loan Repayments claims", js: true, flaky: true do
   let(:one_second_in_minutes) { 1 / 60.to_f }
   let(:two_seconds_in_minutes) { 2 / 60.to_f }