Use testdata.conf for the wxPATH_NORM_LONG test

This file already exists in the test directory, as it's used by another
test, so just use it instead of relying on the existing of mkinstalldirs
in the parent directory, which is not guaranteed as CMake build runs the
tests from a different directory, which is not the immediate child of
the top source directory.

tests/filename/filenametest.cpp

@@ -382,9 +382,9 @@ TEST_CASE("wxFileName::Normalize", "[filename]")
          ).QueryValue("NtfsDisable8dot3NameCreation", &shortNamesDisabled) &&
             !shortNamesDisabled )
     {
-        wxFileName fn("..\\MKINST~1");
+        wxFileName fn("TESTDA~1.CON");
         CHECK( fn.Normalize(wxPATH_NORM_LONG, cwd) );
-        CHECK( fn.GetFullPath() == "..\\mkinstalldirs" );
+        CHECK( fn.GetFullPath() == "testdata.conf" );
     }
     //else: when in doubt, don't run the test
 #endif // __WINDOWS__