scale down the load in ScParallelismTest::testVLOOKUPSUM...

since this method alone takes around 8 minutes in a dbgutil build.

Change-Id: I573545446bd42b7a614d8f5b2d6061c3ec157271
Reviewed-on: https://gerrit.libreoffice.org/69742
Tested-by: Jenkins
Reviewed-by: Dennis Francis <dennis.francis@collabora.com>

sc/qa/unit/parallelism.cxx

@@ -299,7 +299,7 @@ void ScParallelismTest::testVLOOKUPSUM()
 {
     m_pDoc->InsertTab(0, "1");
 
-    const size_t nNumRows = 4096*4;
+    const size_t nNumRows = 2048;
     OUString aTableRef = "$A$1:$B$" + OUString::number(nNumRows);
     for (size_t i = 0; i < nNumRows; ++i)
     {