OTTAWA—The Bank of Canada raised its key interest rate target for the first time since slashing its benchmark rate to its rock-bottom level at the start of the COVID-19 pandemic. The central bank increased its key rate by a quarter of a percentage point to 0.5 percent in a bid to help fight inflation which is at its highest level since 1991. The higher rate is expected to prompt the country’s big banks to raise their prime lending rates, a move that will increase the cost of loans such as variable-rate mortgages that are linked to the benchmark. The Bank of Canada cut its key interest rate to the emergency level of 0.25 percent in March 2020 in an effort to help the economy weather the economic shock of the pandemic. Since then, the economy has rebounded and inflation has jumped with the central bank saying today that it now …