sched: Unify .gitignore

We always use leading '/' in .gitignore entries.

Fixes: d7b2d7c ("sched/cgroup: Add cfs_bandwidth01")
Signed-off-by: Petr Vorel <[email protected]>

Author: pevik

testcases/kernel/sched/cfs-scheduler/.gitignore

@@ -1,2 +1,2 @@
 /hackbench
-cfs_bandwidth01
+/cfs_bandwidth01