Humm, the optimization is not related here. Even if it is not involved (replace 17 with []), the line 4 is reported twice, because RETURN_VALUE is executed after CALL_FINALLY.

  4          10 BUILD_LIST               0
             12 POP_BLOCK
             14 CALL_FINALLY             2 (to 18)
             16 RETURN_VALUE

In 3.7 RETURN_VALUE was the opcode executed at line 4. The stack of blocks was unwinded at interpreted loop implicitly when execute RETURN_VALUE. But in 3.8 calling the finally code is explicit.