Issue #13161: fix doc strings of __i*__ operators

Objects/typeobject.c

@@ -5556,25 +5556,25 @@ static slotdef slotdefs[] = {
     NBSLOT("__index__", nb_index, slot_nb_index, wrap_unaryfunc,
            "x[y:z] <==> x[y.__index__():z.__index__()]"),
     IBSLOT("__iadd__", nb_inplace_add, slot_nb_inplace_add,
-           wrap_binaryfunc, "+"),
+           wrap_binaryfunc, "+="),
     IBSLOT("__isub__", nb_inplace_subtract, slot_nb_inplace_subtract,
-           wrap_binaryfunc, "-"),
+           wrap_binaryfunc, "-="),
     IBSLOT("__imul__", nb_inplace_multiply, slot_nb_inplace_multiply,
-           wrap_binaryfunc, "*"),
+           wrap_binaryfunc, "*="),
     IBSLOT("__imod__", nb_inplace_remainder, slot_nb_inplace_remainder,
-           wrap_binaryfunc, "%"),
+           wrap_binaryfunc, "%="),
     IBSLOT("__ipow__", nb_inplace_power, slot_nb_inplace_power,
-           wrap_binaryfunc, "**"),
+           wrap_binaryfunc, "**="),
     IBSLOT("__ilshift__", nb_inplace_lshift, slot_nb_inplace_lshift,
-           wrap_binaryfunc, "<<"),
+           wrap_binaryfunc, "<<="),
     IBSLOT("__irshift__", nb_inplace_rshift, slot_nb_inplace_rshift,
-           wrap_binaryfunc, ">>"),
+           wrap_binaryfunc, ">>="),
     IBSLOT("__iand__", nb_inplace_and, slot_nb_inplace_and,
-           wrap_binaryfunc, "&"),
+           wrap_binaryfunc, "&="),
     IBSLOT("__ixor__", nb_inplace_xor, slot_nb_inplace_xor,
-           wrap_binaryfunc, "^"),
+           wrap_binaryfunc, "^="),
     IBSLOT("__ior__", nb_inplace_or, slot_nb_inplace_or,
-           wrap_binaryfunc, "|"),
+           wrap_binaryfunc, "|="),
     BINSLOT("__floordiv__", nb_floor_divide, slot_nb_floor_divide, "//"),
     RBINSLOT("__rfloordiv__", nb_floor_divide, slot_nb_floor_divide, "//"),
     BINSLOT("__truediv__", nb_true_divide, slot_nb_true_divide, "/"),