MILAN (Reuters) – Shares in UniCredit shot up as much as 8% on Wednesday, outperforming a sector rebound, after Italy’s No.2 bank detailed its exposure to Russia and confirmed its cash dividends and plans for a share buyback. UniCredit said a worst-case scenario, in which it had to reduce its Russia exposure to zero, would knock 2 percentage points off its Common Equity Tier 1 ratio – a key measure of financial strength which stood just above 15% at the end of last year. Provided that ratio remains above 13% UniCredit said it remained committed to a share buyback of up to 2.6 billion euros ($2…