[CI] Shard FP8 MoE kernels and L4 Humming eval automatically (#61831)

Signed-off-by: Kevin Luu <51931015+khluu@users.noreply.github.com>
Signed-off-by: Thang Nguyen <thangnguyenvn647@gmail.com>
Co-authored-by: Codex <noreply@openai.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

.buildkite/test_areas/kernels.yaml

@@ -890,6 +890,7 @@ steps:
 
 - label: ":nvidia: (H100) [Nightly] DeepEP FP8 MoE Kernels"
   key: kernels-fp8-moe-test-2xh100
+  automatic_shard: true
   timeout_in_minutes: 45
   device: h100
   num_devices: 2
@@ -900,6 +901,7 @@ steps:
   mirror:
     amd:
       label: ":amd: (MI355) DeepEP FP8 MoE Kernels"
+      automatic_shard: true
       dind: false
       device: mi355_2
       timeout_in_minutes: 55

.buildkite/test_areas/lm_eval.yaml

@@ -831,6 +831,7 @@ steps:
 
 - label: ":nvidia: (L4) [Nightly] LM Eval Humming TEMPORARY"
   key: lm-eval-humming-l4
+  automatic_shard: true
   optional: true
   timeout_in_minutes: 90
   device: l4