[CI] Fix schedule trigger bug (#757)

### What this PR does / why we need it?
This PR aims to fix nightly ci
[broken](https://github.com/vllm-project/vllm-ascend/actions/runs/14848150987)
We have a workflow containing multiple triggers:

- push events (to the default branch)
- pull requests (against the default branch)
- scheduled events
Our paths-filter action works great for the first two use-cases,
detecting the context and base to compare against. However, it fails for
scheduled events giving the error `This action requires 'base' input to
be configured or 'repository.default_branch' to be set in the event
payload.`
For the scheduling trigger event, we choose to skip this filter
because we don't need its results:
```
      - name: Check for changes in Speculative Decode
        if: github.event_name != 'schedule'
```

Signed-off-by: wangli <wangli858794774@gmail.com>

.github/workflows/vllm_ascend_test.yaml

@@ -134,6 +134,7 @@ jobs:
 
       # only run test on spec decode when the related code changed
       - name: Check for changes in Speculative Decode
+        if: github.event_name != 'schedule'
         id: filter_spec_decode
         uses: dorny/paths-filter@v3
         with: