Index an enum-value table bug

Nobody has claimed this yet.

### 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

expected the value type of mapping when index

### Actual Behaviour

got an unknown

### Reproduction steps

```lua
---@enum(key) AttrName
local o = {
['hp_max'] = true,
}
local map = {
['hp_max'] = 114514,
}
---@param t table
local function test(t)
--[[
Usage 1: correct
]]
local a = 'hp_max'
local b = t[a] -- expected: number, got: number
print(b)

--[[
Usage 2: incorrect
]]
local c = t['hp_max'] -- expected: number, got: unknown
print(c)

--[[
Usage 3: correct
]]
local d = "hp_grow"
local e = t[d] -- expected: unknown, got: unknown
print(e)
end
test(map)
```

### Additional Notes

_No response_

### Log File

_No response_

Reproduce the report in the LuaLS Visual Studio Code extension on Windows using the supplied Lua snippet and inspect the type-checking path for enum-key table indexing. Compare the diagnostics for the three usages, especially the literal 'hp_max' index. Done means the reported types match the expectations in the reproduction.

Written by the indexing model from the issue text.