Converted exponential backoff to fixed

[tofarr]

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End-user friendly description of the problem this fixes or functionality this introduces.
Converted the exponential backoff to a fixed backoff.

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Summarize what the PR does, explaining any non-trivial design decisions.
This aligns with the other runtime implementations (e.g.: DockerRuntime, RemoteRuntime).

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Link of any specific issues this addresses:

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:2a11c30-nikolaik   --name openhands-app-2a11c30   docker.all-hands.dev/all-hands-ai/openhands:2a11c30