[Bugfix] Use runner_type instead of task in GritLM

[pooyadavoodi]

While the GritLM PR #10816 was merged, #10820 added new type of pooling tasks to vllm. Since GritLM pooling logic relied on the task type, the tests started to fail. This PR is now using runner_type instead of task in the pooling logic.

[github-actions]

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