fix: passing kubernetes compute pool option

[saikonen]

fixes issue with launching kubernetes tasks with a default node_selector. Introduced in #1952

is the else block required at all? the default dict messes up with the value of node_selector being passed to the CLI, where parsing fails.

2024-08-19 12:06:18.037 [1450/start/4611 (pid 74904)] in kube-cli step the node_selector is: {}
2024-08-19 12:06:19.178 [1450/start/4611 (pid 74904)] Kubernetes error:
2024-08-19 12:06:19.178 [1450/start/4611 (pid 74904)] Unable to parse kubernetes list: {}