The Russian economy is now shrinking, and businesses are having more trouble keeping up with debt payments, representing a potentially systemic threat to the country’s bond market. According to data from the central bank this week, GDP contracted 0.5% year over year in the first quarter, far below projections for 1.6% growth, due in part to an increase in the value-added tax the Kremlin imposed to pay for its war on Ukraine. That’s despite a ser…