ci: stop funding devnet, keep only sepolia envs in Ensure Funded Environments

[AztecBot]

What

The "Ensure Funded Environments" workflow was funding the dynamically discovered v*-devnet-* namespaces in addition to the static envs. The only environments still running against sepolia are next-net, testnet and staging-public, so the daily funding job (and the per-env Slack failure alerts, e.g. the recent devnet failure) should no longer cover devnet.

Changes

• ensure-funded-environments.yml: drop the active-devnet discovery step and the Node setup it required; the funding matrix is now just the three static sepolia envs (staging-public, next-net, testnet). Renamed the prep job discover → build-matrix since it no longer discovers anything.
• ensure-funded-environment.yml: remove devnet from the manual workflow_dispatch environment dropdown.

staging-ignition was not in the funded-environments list, so no change was needed for it — the resulting funded set matches the requested next-net, testnet, staging-public.

Note: spartan/scripts/get_active_devnets.ts is left in place (it shares devnet_utils.ts with the still-used devnet deploy scripts); it is simply no longer invoked by the funding workflow.

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Created by claudebox · group: slackbot