[TASK] Stabilize FileClipboardCest ac test

Wait for the drop down to be ready
before clicking around on it.

Resolves: #104585
Releases: main, 12.4, 11.5
Change-Id: I9fa86d99b02c74bcc0f9efebce8fc4c2f8e54af5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85578


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>