Fix failing browser_ui/3_create/web_ide/review_merge_request_spec - Update to focus on new tab

What does this MR do and why?

Fix the failure in: #381530 (closed) through updating the spec. The spec was failing because clicking on web_ide on merge_request opens to a new tab now. Spec was updated with page.driver.browser.switch_to.window(page.driver.browser.window_handles.last) so the driver can continue on that tab.

How to set up and validate locally

Run: bundle exec bin/qa Test::Instance::All http://gdk.test:3000/ qa/specs/features/browser_ui/3_create/web_ide/review_merge_request_spec.rb

MR acceptance checklist

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