JOHANNESBURG — While the United States and Europe have pressured countries to turn their backs on Russia over its invasion of Ukraine, South Africa has bolstered its longtime alliance with Moscow — a friendship that dates to the struggle against apartheid. Russia and South Africa, along with China, are scheduled on Friday to start 11 days of joint military exercises off the east coast of South Africa that will include a Russian warship bearing the letters Z and V — Russia’s patriotic symbols for its war in Ukraine — and…