tests/.gitignore: add ksysent.h

tests/ksysent.h is a generated file listed in CLEANFILES.
This change complements commit v4.10-566-gbab4ef4.

* tests/.gitignore: Add ksysent.h.
diff --git a/tests/.gitignore b/tests/.gitignore
index 6cc56cc..bfd34b4 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -38,6 +38,7 @@
 ipc_sem
 ipc_shm
 ksysent
+ksysent.h
 llseek
 lseek
 lstat