selftests/vm: add local_config.h and local_config.mk to .gitignore

Add local_config.h and local_config.mk to .gitignore to avoid accidentally
checking it in.

Link: https://lkml.kernel.org/r/20221103005754.205420-1-zhaogongyi@huawei.com


Signed-off-by: Zhao Gongyi <zhaogongyi@huawei.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>