fix io_test (#48097)

packages/flutter_tools/test/general.shard/base/io_test.dart

diff --git a/packages/flutter_tools/test/general.shard/base/io_test.dart b/packages/flutter_tools/test/general.shard/base/io_test.dart
index 4d587fd..a1eabf2 100644
--- a/packages/flutter_tools/test/general.shard/base/io_test.dart
+++ b/packages/flutter_tools/test/general.shard/base/io_test.dart
@@ -77,6 +77,7 @@
     setExitFunctionForTests((int value) {});
 
     expect(() => exit(0), returnsNormally);
+    restoreExitFunction();
   });
 
   test('test_api defines the Declarer in a known place', () {