[CI] Do not drop ready label when PR is merge conflict (#3173)

### What this PR does / why we need it?
`ready` label now is used for trigger full e2e test now. If a PR is
ready and merge conflict then, no need to drop the ready label.

### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Just a github action change. No need for function test.

- vLLM version: v0.10.2
- vLLM main:
52d0cb8458

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

.github/workflows/label_merge_conflict.yml

@@ -16,6 +16,5 @@ jobs:
         uses: eps1lon/actions-label-merge-conflict@v3
         with:
           dirtyLabel: "merge-conflicts"
-          removeOnDirtyLabel: "ready"
           repoToken: "${{ secrets.GITHUB_TOKEN }}"
           commentOnDirty: "This pull request has conflicts, please resolve those before we can evaluate the pull request."