selftests/exec: add generated files to .gitignore

Add generated files non-regular and null-argv to .gitignore file.
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/exec/.gitignore

@@ -7,6 +7,8 @@ execveat.moved
 execveat.path.ephemeral
 execveat.ephemeral
 execveat.denatured
+non-regular
+null-argv
 /load_address_*
 /recursion-depth
 xxxxxxxx*