Merge branch 'fix-qmap-lookup-task-ctx' into scx-cid-base

Pull to receive e6958df85e27 ("tools/sched_ext: scx_qmap: Silence
task_ctx lookup miss") plus the 4fe985292709 rhashtable fix carried on
for-7.1-fixes.

Conflict resolution: for-7.2 refactored qmap into arena-backed task_ctx
slabs after for-7.1-fixes branched. The conflict is across three sites
in scx_qmap.bpf.c - lookup_task_ctx(), qmap_dispatch()'s @prev branch,
and task_qdist() - all of which need to drop the scx_bpf_error on
storage miss. Keep for-7.2's arena-refactored structure (TOUCH_ARENA,
struct task_ctx_stor_val, task_ctx_t, the fifo helpers) and apply the
same semantic change on that side: lookup_task_ctx() returns NULL
silently, and its callers in qmap_dispatch() / task_qdist() skip
gracefully on NULL.

Signed-off-by: Tejun Heo <tj@kernel.org>