Reassigning table upvalue errors with new solver

[Ketasaja]

Tested on 0.635, with no errors in non-strict mode.

--!strict
local t: {[string]: string} = {}

local function f()
	t = t --[[ TypeError: Type function instance t1 where t1 = union<{ [string]: string }, t1> is uninhabited
	This is likely to be a bug, please report it at https://github.com/luau-lang/luau/issues ]]
end

t = t