@generic return ignores question mark

還沒有人認領這個 Issue。

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

Visual Studio Code Extension (sumneko.lua)

### Which OS are you using?

Windows

### What is the issue affecting?

Type Checking

### Expected Behaviour

Type of `y` in example below is `integer?`

### Actual Behaviour

Type of `y` in example below is `integer`

### Reproduction steps

```lua
---@generic T
---@param test T
---@return T?
function Func(test)
end

--- @return integer?
function Func2()
end

local x = 0
local y = Func(x)
local z = Func2()
```

### Additional Notes

`T | nil` works as a workaround.

### Log File

_No response_

在 Visual Studio Code 擴充功能中重現 Lua 程式碼片段，並檢查 y 和 z 的推斷型別，將 T? 與 T | nil 替代方案進行比較。完成標準是泛型 @return T? 保留 nil，使 y 為 integer?，而現有的 Func2 結果仍為 integer?。

由索引模型根據 Issue 內容生成。