Fix flaky repository settings spec

What does this MR do and why?

The test was failing intermittently because the test would input the URL and submit the data faster than the JavaScript was able to update the internal field. This caused a blank URL to be submitted on occasion. To make this spec more reliable, we now ensure the hidden URL field is updated with the right value before clicking the "Save changes" button.

Closes #337394 (closed)

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