Draft: Clarifying that indirectly merged branches will also be deleted

What does this MR do and why?

Closes #371977 (closed)

Changes the prompt when clicking the Delete merged branches button from Repository -> Branches

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Check that the prompt has been changed from Deleting the merged branches cannot be undone. Are you sure? to Deleting directly and indirectly merged branches cannot be undone. Are you sure?

MR acceptance checklist

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