[Fix #12154] Fix incorrect diagnosticProvider value of LSP

[koic]

Fixes #12154.

This PR fixes incorrect diagnosticProvider value of LSP.

diagnosticProvider cannot accept true as below. This PR replaces the originally acceptable value.

/**
 * The server has support for pull model diagnostics.
 *
 * @since 3.17.0
 */
diagnosticProvider?: DiagnosticOptions | DiagnosticRegistrationOptions;

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialize

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