ltp: make fork05 test optional

The modify_ldt syscall is optional, so this test should be as well,
since it depends on that syscall.

Bug: 138821368
Change-Id: Idea98d531db74c3d1bae7a00ba8475643daa4025
diff --git a/ltp/configs/stable_tests.py b/ltp/configs/stable_tests.py
index c260b60..a96153d 100644
--- a/ltp/configs/stable_tests.py
+++ b/ltp/configs/stable_tests.py
@@ -767,8 +767,8 @@
     ('syscalls.fork03_64bit', True),
     ('syscalls.fork04_32bit', True),
     ('syscalls.fork04_64bit', True),
-    ('syscalls.fork05_32bit', True),
-    ('syscalls.fork05_64bit', True),
+    ('syscalls.fork05_32bit', False),
+    ('syscalls.fork05_64bit', False),
     ('syscalls.fork06_32bit', True),
     ('syscalls.fork06_64bit', True),
     ('syscalls.fork07_32bit', True),