move stress.xls to stress.xlsx (#1021)

Author: pjfanning

poi-integration/src/test/java/org/apache/poi/stress/TestAllFiles.java

@@ -103,7 +103,7 @@ public class TestAllFiles {
         // invalid files
         "spreadsheet/bug69769.xlsx",
 
-        // NOTE: Expected failures should usually be added in file "stress.xls" instead
+        // NOTE: Expected failures should usually be added in file "stress.xlsx" instead
         // of being listed here in order to also verify the expected exception details!
     };
 
@@ -161,7 +161,7 @@ public class TestAllFiles {
 
     public static Stream<Arguments> allfiles(String testName) throws IOException {
         StressMap sm = new StressMap();
-        sm.load(new File(ROOT_DIR, "spreadsheet/stress.xls"));
+        sm.load(new File(ROOT_DIR, "spreadsheet/stress.xlsx"));
 
         boolean noScratch = Boolean.getBoolean("scratchpad.ignore");