[FIX] web_tour: place tooltip above dropdown-menu
[FIX] web_tour: place tooltip above dropdown-menu

Before this commit, a tip on a dropdown menu item was visible.

This is due to the positioning of the tip, which was on the
dropdown-menu (because it has overflow `auto`). The tip was
appended on the dropdown-menu, and may overflow as a result.

This commit handles specifically the case of dropdown-menu,
so that dropdown-menu is never a candidate for the placement
of the tip.

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