KYIV— Ukrainian President Volodymyr Zelenskyy will skip a key post-war recovery conference in Poland this week, Kyiv said Tuesday, amid a spiraling diplomatic spat between the allies over World War II memory. Zelenskyy infuriated Warsaw last month by naming a military unit after the nationalist Ukrainian Insurgent Army (UPA), a group that took part in massacres against Poles during World War II.Poland's nationalist president Karol Nawrocki responded by stripping Zelenskyy of Warsaw's highest honor, the Order of the White Eagle, prompting several top Ukrainian officials to hand back their Polish awards. The row threatens to overshadow the Ukraine Recovery Conference,...