[eprh] Type configs.flat more strictly (#34950)

Addresses #34801 where `configs.flat` is possibly undefined as it was
typed as a record of arbitrary string keys.

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Author: poteto

packages/eslint-plugin-react-hooks/src/index.ts

@@ -71,7 +71,10 @@ const configs = {
     plugins,
     rules: recommendedLatestRuleConfigs,
   },
-  flat: {} as Record<string, ReactHooksFlatConfig>,
+  flat: {} as {
+    recommended: ReactHooksFlatConfig;
+    'recommended-latest': ReactHooksFlatConfig;
+  },
 };
 
 const plugin = {