duplicate field error when setting a field to a function in an if/else

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### 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?

Diagnostics/Syntax Checking

### Expected Behaviour

No duplicate field error

### Actual Behaviour

``` local t = {}
if x then
t.s = function() return 1 end
else
t.s = function() return 2 end
end
```
This is not a duplicate field and should not be an error

### Reproduction steps

``` local t = {}
if x then
t.s = function() return 1 end
else
t.s = function() return 2 end
end
```
Write that into the editor. See error as indicated above.

### Additional Notes

v3.6.4

### Log File

[file_c%3A_Users_User_AppData_Roaming_Factorio_mods_space-exploration.log](https://github.com/sumneko/lua-language-server/files/10316714/file_c.3A_Users_User_AppData_Roaming_Factorio_mods_space-exploration.log)

Reproduce the diagnostic in the Visual Studio Code extension using the provided conditional-assignment snippet, focusing on the Diagnostics/Syntax Checking entry point. Trace why the two branch assignments are reported as a duplicate field, then verify that the same example no longer produces the error.

Written by the indexing model from the issue text.