`bench-pr-comment.yml` fails on the first run

Example: https://github.com/lurk-lab/arecibo/pull/352#issuecomment-1984696614

When run for the first time in a PR, the workflow fails with
```
Error: Unable to process file command 'env' successfully.
Error: Invalid format '
'
```

This is likely a newline or whitespace issue to be debugged. However, the workflow runs correctly on subsequent `!benchmark` runs for some reason.

从 .github/workflows/bench-pr-comment.yml 开始，复现 issue 中描述的第一次 !benchmark 运行。检查 workflow 如何处理 env file command 及其换行或空白；当第一次 benchmark 运行在没有报告的格式错误的情况下成功，并且后续运行继续正常工作时，即表示完成。

由索引模型根据 Issue 内容生成。