[DF] Better name for test file

[eguiraud]

NeverWrittenOut.root is actually written out (because the exception is thrown during the event loop).

Change the file name so that it's deleted at the end of the test.

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds

[phsft-bot]

Starting build on ROOT-debian10-i386/soversion, ROOT-performance-centos8-multicore/cxx17, ROOT-ubuntu18.04/nortcxxmod, ROOT-ubuntu2004/python3, mac1015/cxx17, mac11/cxx14, windows10/cxx14 How to customize builds

[phsft-bot]

Build failed on windows10/cxx14. Running on null:C:\build\workspace\root-pullrequests-build See console output.

Errors:

• [2022-08-11T08:57:29.188Z] C:\build\workspace\root-pullrequests-build\root\interpreter\llvm\src\lib\Transforms\Scalar\LoopStrengthReduce.cpp(5771,1): fatal error C1060: compiler is out of heap space [C:\build\workspace\root-pullrequests-build\build\interpreter\llvm\src\lib\Transforms\Scalar\LLVMScalarOpts.vcxproj]
• [2022-08-11T08:57:38.581Z] C:\build\workspace\root-pullrequests-build\root\interpreter\llvm\src\lib\CodeGen\SelectionDAG\FunctionLoweringInfo.cpp(546,1): fatal error C1060: compiler is out of heap space [C:\build\workspace\root-pullrequests-build\build\interpreter\llvm\src\lib\CodeGen\SelectionDAG\LLVMSelectionDAG.vcxproj]

[phsft-bot]

Build failed on ROOT-performance-centos8-multicore/cxx17. Running on olbdw-01.cern.ch:/data/sftnight/workspace/root-pullrequests-build See console output.

Failing tests:

• projectroot.runtutorials.tutorial_roofit_rf408_RDataFrameToRooFit