[CI] Avoid lint and ut for PR push (#5762)

1. Don't run lint and ut again once the PR is merged to save CI resource
2. Update codecov every 4 hour
3. rename `model_downloader` to suitable name
4. update schedule job to better time.

- vLLM version: v0.13.0
- vLLM main:
2f4e6548ef

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

.github/workflows/schedule_nightly_image_build.yaml

@@ -2,7 +2,8 @@ name: Nightly Image Build Schedule
 
 on:
   schedule:
-    - cron: '0 0,4,8,12,15 * * *'
+    # UTC+8: 20pm, 23pm
+    - cron: '0 12,15 * * *'
 
 # This workflow builds and pushes Docker images for nightly-ci
 # It will be built base on the quay.io/ascend/vllm-ascend:main