Test: don't discard result of QFile::open

QVERIFY that the file could be opened, fail the test if it couldn't.

Pick-to: 6.9
Change-Id: Iab9b819e70b71fade6a58286edff8e022748d9f6
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
(cherry picked from commit 33dc247b6a553a5e4a6038189359d459d9019edf)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

tests/auto/corelib/io/qfileinfo/tst_qfileinfo.cpp

@@ -1995,7 +1995,7 @@ void tst_QFileInfo::brokenShortcut()
     QString linkName("borkenlink.lnk");
     QFile::remove(linkName);
     QFile file(linkName);
-    file.open(QFile::WriteOnly);
+    QVERIFY(file.open(QFile::WriteOnly));
     file.write("b0rk");
     file.close();