CppunitTest_sw_uwriter: make rng used in this test repeatable

So in case the test fails, it's possible to see the same failure
multiple times.

Change-Id: Ic573807967b004bb7650ffb3614f5006db34080e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100137
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
diff --git a/sw/qa/core/uwriter.cxx b/sw/qa/core/uwriter.cxx
index 079f7e3..a2b5e99 100644
--- a/sw/qa/core/uwriter.cxx
+++ b/sw/qa/core/uwriter.cxx
@@ -43,6 +43,7 @@
#include <sfx2/docfile.hxx>

#include <xmloff/odffields.hxx>
#include <osl/process.h>

#include <breakit.hxx>
#include <doc.hxx>
@@ -1075,6 +1076,10 @@ getRandomPosition(SwDoc *pDoc, int /* nOffset */)

void SwDocTest::randomTest()
{
    OUString aEnvKey("SAL_RAND_REPEATABLE");
    OUString aEnvValue("1");
    osl_setEnvironment(aEnvKey.pData, aEnvValue.pData);

    CPPUNIT_ASSERT_MESSAGE("SwDoc::IsRedlineOn()", !m_pDoc->getIDocumentRedlineAccess().IsRedlineOn());
    RedlineFlags modes[] = {
        RedlineFlags::On,