`duplicate-set-field` is reading from CoreLibs even though `diagnostics.libraryFiles` is set to 'Disable'

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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?

Formatting

### Expected Behaviour

I do not see a warning for `duplicate-set-field` in my project.

### Actual Behaviour

Hi

Thanks for this plugin. I am getting warning for `duplicate-set-field` on this line:

`function playdate.update()`

and the duplicate is in the `CoreLibs` folder here:

`...\PlaydateSDK\CoreLibs\__stub.lua`

I have set the CoreLibs folder to be ignored by the code checker:

`"Lua.diagnostics.libraryFiles": "Disable",`

Is this the expected behaviour?

### Reproduction steps

1. Install Lua language server plugin
2. Set `"Lua.diagnostics.libraryFiles": "Disable",`
3. Create `main.lua`
4. Add the line `function playdate.update()` to `main.lua`
5. Observe warning:
```
"resource": "/e:/dev/miner/Source/main.lua",
"owner": "_generated_diagnostic_collection_name_#0",
"code": "duplicate-set-field",
"severity": 4,
"message": "Duplicate field `update`.",
"source": "Lua Diagnostics.",
"startLineNumber": 72,
"startColumn": 10,
"endLineNumber": 72,
"endColumn": 25,
"relatedInformation": [
{
"startLineNumber": 5,
"startColumn": 10,
"endLineNumber": 5,
"endColumn": 25,
"message": ".twopolefilter.s",
"resource": "/e:/devtools/PlaydateSDK/CoreLibs/__stub.lua"
}
]
}]
```

### Additional Notes

_No response_

### Log File

_No response_

Reproduce the warning using main.lua, the playdate.update() line, and the Lua.diagnostics.libraryFiles setting set to Disable; compare the diagnostic with CoreLibs/__stub.lua. Trace how duplicate-set-field diagnostics handle library files and verify the setting’s documented behavior. Done means the observed warning behavior is consistent with the intended configuration.

Written by the indexing model from the issue text.