Custom __pairs expects only 1 return value

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### How are you using the lua-language-server?

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

Linux

### What is the issue affecting?

Type Checking

### Expected Behaviour

I expected no warnings

### Actual Behaviour

There is a redundant return value warning

### Reproduction steps

Here's an example where string paths are transformed to their package.loaded value

```lua
local imports = {
mod1 = "src.mod1",
mod2 = "src.mod2"
}

return setmetatable({}, {
__pairs = function(_)
local iter = pairs(imports)

local newiter = function (table, index)
local k, path = iter(table, index)

return k, package.loaded[path]
end

--- LuaLS is wrong here
---@diagnostic disable-next-line:redundant-return-value
return newiter, imports, nil
end
})
```

### Additional Notes

https://www.lua.org/pil/7.3.html

### Log File

_No response_

Reproduce the warning in the LuaLS Visual Studio Code extension using the provided setmetatable and __pairs example on Linux. Start with the type-checking handling for __pairs and compare it with the Lua 7.3 reference linked in the issue. Done means the example no longer reports a redundant return value warning.

Written by the indexing model from the issue text.