Reflect that env will set on scheduler too

[CarterFendley]

Minor docs change to reflect that the env parameter of KubeCluster will set the environment variables on the scheduler (in addition to workers).

See that this is the case here in make_cluster_spec(...), that function's doc string is correct. But if you are like me you may only look at the doc string on KubeCluster in an LSP annotation / on the docs

[jacobtomlinson]

Thanks!

[CarterFendley]

Thank you!