`@overload` return union unexpected behaviour

Nobody has claimed this yet.

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

NeoVim

### Which OS are you using?

Windows

### What is the issue affecting?

Type Checking, Diagnostics/Syntax Checking

### Expected Behaviour

Type of `r1` = `EA|0`
Not warning: probably `nil`

### Actual Behaviour

Type of `r1` = `integer|EA|0`
Warning: probably `nil`

### Reproduction steps

1. Create file `test.lua`
2. Fill
```lua
---@enum EA
local EA = {
a = 1,
b = 2,
}
local ab = 0
---@overload fun(): 0
---@overload fun(): EA, [string]
local function fua()
if ab == 0 then
return 0
else
return EA[ab] or EA.a, { "aa" }
end
end

local r1, r2 = fua()

if r1 == 0 then
print(0)
else
print(r2[1])
end
```
4. See type of `r1`
5. See `Need check nil` at line 22

### Additional Notes

Maybe duplicate of #1456


### Log File

[Log file](https://github.com/user-attachments/files/18804669/file_F_.23utils_lua_vie.nlisp.log)

Start by reproducing the report in test.lua with the supplied @overload example and inspect the inferred types and diagnostic at line 22. Done means r1 is inferred as EA|0 and the nil warning is no longer reported for the shown control flow.

Written by the indexing model from the issue text.