Dismiss modal after increasing access level

What does this MR do and why?

After updating a user's access level in a group, this checks if a confirmation modal appears, and if so, it clicks "ok".

This accounts for the change in !105613 (merged) that's behind the feature flag show_overage_on_role_promotion, which caused ee/browser_ui/10_govern/group/group_audit_logs_1_spec.rb to fail: #417067 (closed)

See also #385496 (comment 1459186375)

How to set up and validate locally

In rails console, enable the feature flag

Feature.enable(:show_overage_on_role_promotion)

Run the test from the qa directory:

bundle install
export WEBDRIVER_HEADLESS=false # If you'd like to watch the test in action
export QA_GITLAB_URL="http://gdk.test:3000" # Only needed if GDK is not running on http://127.0.0.1:3000
bundle exec rspec qa/specs/features/ee/browser_ui/10_govern/group/group_audit_logs_1_spec.rb

If you disable the feature flag and rerun the test it should still pass.

MR acceptance checklist

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