The third installment in Ken Loach’s unofficial trilogy of films set in austerity-era northeastern England, “The Old Oak” looks at what happens when immigrant families from Syria arrive in an economically depressed former coal-mining town near Durham. Set in 2016 — the year many Syrian immigrants first came to Britain — and said to be the final movie from the 87-year-old social realist filmmaker, “Oak” joins Loach’s “I, Daniel Blake” (2016) and “Sorry We Missed You” (2019) in the tradition of his career-long compassion for the marginalized and forgotten. It is unmistakably a Loach film: taciturn yet forthright (occasionally to the point of obviousness), examining life in the cracks of a fractured society with deep compassion, plain-spoken anger and, perhaps more so than in the previous two films, a shot of hope.