scripts/test_list: Don't log missing testlist

When tests are compiled conditionally and compilation flag is set
to false they have no binaries in the build directory. As testlist
is built from .c source file list, unnecessary warnings about missing
.testlist files are produced.

Avoid this warnings by skipping processing testlists for which binaries
weren't produced.

Cc: Dominik Grzegorzek <dominik.grzegorzek@intel.com>
Cc: Katarzyna Piecielska <katarzyna.piecielska@intel.com>
Cc: Christoph Manszewski <christoph.manszewski@intel.com>
Reviewed-by: Christoph Manszewski <christoph.manszewski@intel.com>
Link: https://lore.kernel.org/r/20240919081603.523299-1-zbigniew.kempczynski@intel.com


Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>