Fix flaky test (#16874)

config/file_test.go

@@ -927,7 +927,12 @@ func TestFileStoreWatcherEmitter(t *testing.T) {
 		cfgData, err := config.MarshalConfig(minimalConfig)
 		require.NoError(t, err)
 
-		ioutil.WriteFile(path, cfgData, 0644)
+		f, err := os.OpenFile(path, os.O_WRONLY, 0644)
+		require.NoError(t, err)
+		defer f.Close()
+		_, err = f.Write(cfgData)
+		require.NoError(t, err)
+
 		require.True(t, wasCalled(called, 5*time.Second), "callback should have been called when config written")
 	})