try to stabilize test suite

Author: rbri

src/test/java/org/htmlunit/html/HtmlFileInputTest.java

@@ -76,6 +76,7 @@ public void contentTypeHeader() throws Exception {
      * @throws Exception if an error occurs
      */
     @Test
+    @Retry
     @Alerts("Content-Disposition: form-data; name=\"myInput\"; filename=\"\"")
     public void empty() throws Exception {
         final String htmlContent