sched_ext: Fix typos in comments

sched_ext: Fix typos in comments

Fix five typos across three files:

- kernel/sched/ext.c: 'monotically' -> 'monotonically' (line 55)
- kernel/sched/ext.c: 'used by to check' -> 'used to check' (line 56)
- kernel/sched/ext.c: 'hardlockdup' -> 'hardlockup' (line 3881)
- kernel/sched/ext_idle.c: 'don't perfectly overlaps' ->
  'don't perfectly overlap' (line 371)
- tools/sched_ext/scx_flatcg.bpf.c: 'shaer' -> 'share' (line 21)

Signed-off-by: zhidao su <suzhidao@xiaomi.com>
Signed-off-by: Tejun Heo <tj@kernel.org>