Fix recently added auto test of text layout overflow

Ignore width of trailing space.

Pick-to: 6.1 6.0 5.15
Fixes: QTBUG-91038
Change-Id: I74e278366a2c3b170335738bf6d6ee23933b361a
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

tests/auto/gui/text/qtextlayout/tst_qtextlayout.cpp

@@ -1907,7 +1907,8 @@ void tst_QTextLayout::longText()
                 break;
         }
         layout.endLayout();
-        QVERIFY(layout.maximumWidth() <= QFIXED_MAX);
+        QFontMetricsF fm(layout.font());
+        QVERIFY(layout.maximumWidth() - fm.horizontalAdvance(' ') <= QFIXED_MAX);
     }
 }