Fix tst_qaccessibility::textEditTest for some screen resolutions

On a high resolution display the test will potentially create a text
edit that introduces line breaks and these make it fail then.

Change-Id: I38807a9b3b511478a1742c4422a97c1cb3395a02
Reviewed-by: Jan Arve Sæther <jan-arve.saether@theqtcompany.com>

tests/auto/other/qaccessibility/tst_qaccessibility.cpp

@@ -1748,6 +1748,7 @@ void tst_QAccessibility::textEditTest()
     for (int pass = 0; pass < 2; ++pass) {
         {
         QTextEdit edit;
+        edit.setMinimumSize(600, 400);
         setFrameless(&edit);
         int startOffset;
         int endOffset;