Increases duration to wait for total storage text to update

What does this MR do and why?

Increases the wait time for the total storage size calculation to appear. The total storage size takes time to appear on the page even thought the table underneath for the individual projects might already have the total so I'm increasing the wait time for the larger total size count above the page to update.

Related: #421526 (closed)

How to set up and validate locally

This spec needs to be run against Staging. To run the spec, run bundle exec rspec qa/specs/features/ee/browser_ui/11_fulfillment/utilization/free_namespace_storage_spec.rb

MR acceptance checklist

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