tst_QFile::largeUncFileSupport is flaky in Windows

cd /d .. && call C:\Users\qt\work\qt\qtbase\tests\auto\corelib\io\qfile\test\target_wrapper.bat  tst_qfile.exe largeUncFileSupport
********* Start testing of tst_QFile *********
Config: Using QtTest library 5.9.2, Qt 5.9.2 (i386-little_endian-ilp32 shared (dynamic) release build; by GCC 5.3.0)
PASS   : tst_QFile::initTestCase()
FAIL!  : tst_QFile::largeUncFileSupport() 'file.open(QIODevice::ReadOnly)' returned FALSE. (Could not open "\\qt-test-server.qt-test-net\testsharelargefile\file.bin": The process cannot access the file because it is being used by another process.)
..\tst_qfile.cpp(1608) : failure location
PASS   : tst_QFile::cleanupTestCase()
Totals: 2 passed, 1 failed, 0 skipped, 0 blacklisted, 60018ms