UsePatternMatching wrong fix template

[marodev]

The following pattern should't be detected or fixed in a different way:

IborCoupon c = coupon as IborCoupon;
Utils.QL_REQUIRE(c != null, () => "IborCoupon required");

Current behaviour:

Utils.QL_REQUIRE(coupon is IborCoupon c, () => "IborCoupon required");