Second QCoreApplication apparently can lead to test failures

[jpfeuffer]

https://github.com/OpenMS/OpenMS/blame/9a45bd1e7dd9be3f9bb073d04c22c5ced79688e5/src/topp/IDFileConverter.cpp#L826

From Discord:

Command: "C:/Users/OpenMS_Windows64/bin/Debug/IDFileConverter.exe" "-in" "IDMerger_6_output1.oms" "-out" "IDMerger_6_output2.tmp" "-out_type" "idXML"
Directory: C:/Users/OpenMS_Windows64/src/tests/topp
"TOPP_IDMerger_6_out1" start time: Sep 06 20:17 Eastern Daylight Time
Output:
----------------------------------------------------------
ASSERT failure in QCoreApplication: "there should be only one application object", file kernel\qcoreapplication.cpp, line 772
<end of output>

of course related to #5781