kunit: executor: Fix a memory leak on failure in kunit_filter_tests

kunit: executor: Fix a memory leak on failure in kunit_filter_tests

It's possible that memory allocation for 'filtered' will fail, but for the
copy of the suite to succeed. In this case, the copy could be leaked.

Properly free 'copy' in the error case for the allocation of 'filtered'
failing.

Note that there may also have been a similar issue in
kunit_filter_subsuites, before it was removed in "kunit: flatten
kunit_suite*** to kunit_suite** in .kunit_test_suites".

This was reported by clang-analyzer via the kernel test robot, here:
https://lore.kernel.org/all/c8073b8e-7b9e-0830-4177-87c12f16349c@intel.com/

And by smatch via Dan Carpenter and the kernel test robot:
https://lore.kernel.org/all/202207101328.ASjx88yj-lkp@intel.com/

Fixes: a02353f49162 ("kunit: bail out of test filtering logic quicker if OOM")
Reported-by: kernel test robot <yujie.liu@intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>