[CI] Remove workflow_dispatch and change schedule time (#1056)

### What this PR does / why we need it?

- Remove workflow_dispatch 
-  Change schedule time to 2:00 UTC+8
### Does this PR introduce _any_ user-facing change?


### How was this patch tested?
CI passed

---------

Signed-off-by: wangli <858794774@qq.com>
Co-authored-by: wangli <858794774@qq.com>

Author: Potabk

.github/workflows/nightly_benchmarks.yaml

@@ -20,9 +20,8 @@ name: 'Benchmarks / Performance'
 
 on:
   schedule:
-    # Run at 24:00 everyday
-    - cron: '00 16 * * *'
-  workflow_dispatch:
+    # Run at 02:00 everyday
+    - cron: '00 18 * * *'
 
   pull_request:
     types: [ labeled ]