Add regression test

tests/cases/compiler/genericFunctionInference2.ts

@@ -0,0 +1,15 @@
+// Repro from #30685
+
+type Reducer<S> = (state: S) => S;
+declare function combineReducers<S>(reducers: { [K in keyof S]: Reducer<S[K]> }): Reducer<S>;
+
+type MyState = { combined: { foo: number } };
+declare const foo: Reducer<MyState['combined']['foo']>;
+
+const myReducer1: Reducer<MyState> = combineReducers({
+    combined: combineReducers({ foo }),
+});
+
+const myReducer2 = combineReducers({
+    combined: combineReducers({ foo }),
+});