Make error message more verbose in QML test test_loadProgress

If the verify(loadProgressMin <= loadProgress) fails, the output was
not verbose enough. The additional outputs will tell us more about
what caused the test to fail.

Task-number: QTBUG-61815
Change-Id: Ia9b45ef4f09a5b25a344e423a7b0c61d5d430542
Reviewed-by: Kai Koehne <kai.koehne@qt.io>

tests/auto/quick/qmltests/data/tst_loadProgress.qml

@@ -71,7 +71,8 @@ TestWebEngineView {
             var loadProgressMin = 0
             for (var i in loadProgressArray) {
                 var loadProgress = loadProgressArray[i]
-                verify(loadProgressMin <= loadProgress)
+                if (loadProgressMin > loadProgress)
+                    fail("Invalid sequence of progress-values: " + loadProgressArray)
                 loadProgressMin = loadProgress
             }
         }