fix: correct breaking deprecation of FlatConfig type (#19826)

fix: correct deprecation of FlatConfig type

Author: mostpinkest

lib/types/index.d.ts

@@ -1831,7 +1831,7 @@ export namespace Linter {
 	}
 
 	/** @deprecated  Use `Config` instead of `FlatConfig` */
-	type FlatConfig = Config;
+	type FlatConfig<Rules extends RulesRecord = RulesRecord> = Config<Rules>;
 
 	type GlobalConf =
 		| boolean

tests/lib/types/types.test.ts

@@ -2135,6 +2135,12 @@ let flatConfig!: Linter.FlatConfig;
 config = flatConfig;
 flatConfig = config;
 
+let configWithRules!: Linter.Config<ESLintRules>;
+let flatConfigWithRules!: Linter.FlatConfig<ESLintRules>;
+configWithRules = flatConfigWithRules;
+flatConfigWithRules = configWithRules;
+flatConfigWithRules.rules; // $ExpectType Partial<ESLintRules> | undefined
+
 // #endregion Config
 
 // #region Plugins