Incorrect 'Illegal override' when using multiple return values in combination with inheritance

[pouwelsjochem]

Environment

name	version
IDEA version	IC2020.3
Luanalysis version	1.2.2
OS	MacOS Big Sur

What are the steps to reproduce this issue?

local function createMyObject()
    local vehicle = {} ---@class Vehicle
    vehicle.mySuperObject = vehicle

    function vehicle:getVehicle()
        return vehicle
    end
    function vehicle:getVehicleAndSomethingElse()
        return vehicle, true
    end

    return vehicle
end

local function createMyObjectSubClass()
    local car = {} ---@class Car : Vehicle

    function car:getVehicle()
        return car
    end
    function car:getVehicleAndSomethingElse() -- Illegal override of "getVehicleAndSomethingElse". Type mismatch. Required: 'fun(): Vehicle, true' Found: 'fun(): Car, true'
        return car, true
    end
    function car:getVehicleAndSomethingElse()
        return car.mySuperObject, true
    end

    return car
end

What happens?

The first override of getVehicleAndSomethingElse gets an error, while the getVehicle override doesn't while they effectively have the same signature except for one returning multiple values.

What were you expecting to happen?

The first override of getVehicleAndSomethingElse to correctly resolve its type inheritance.

Any other comments?

This might be related to #44, but might also be an addition to it. Using something similar to #44's example will also only give the incorrect 'Illegal override' on the getStringAndSomethingElse method.

    function vehicle:getString()
        return string.upper("a")
    end
    function vehicle:getStringAndSomethingElse()
        return string.upper("a"), true
    end
    function car:getString()
        return "A"
    end
    function car:getStringAndSomethingElse()
        return "A", true
    end