Add automated test for "Move only parent"

The manual test is here: Move only parent

Existing automated coverage

• RenamePageIT#renamePageCheckConfirmationPreserveChildrenUpdateLinksSetAutoRedirect: Same Move/Rename UI flow from page 1/2 to parent A.B, but with "Preserve children" checked (the opposite case).
• MoveJobTest#moveDocumentToSpaceHome: Unit test: non-deep move of a single document (children not moved), mocked model bridge.
• RenameJobTest#renameDocument: Unit test: non-deep rename of a single document.

Missing automated coverage

• Create 1/2/3/4 and A/B with every page existing
• On page 2 open More Actions > Move / Rename, select B in the New Location tree and uncheck "Preserve children" (RenamePage#setPreserveChildren(false)), click Rename
• Assert A/B/2 exists
• Assert 1/2/3 and 1/2/3/4 still exist and are reachable at their old URLs

Suggested location: xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-test/xwiki-platform-flamingo-skin-test-docker/src/test/it/org/xwiki/flamingo/test/docker/RenamePageIT.java

Found by comparing the XWiki 18.4.4 manual test runs against the automated tests on master (a0055f10a1a).