Fix Node 20 deprecation

[evsok]

Fix Node 20 deprecation in vat workflow

Summary

GitHub is retiring the Node 20 action runtime; actions bundling a Node 20 entrypoint emit deprecation warnings today and will eventually stop running. This PR bumps every JavaScript action to the version that ships a Node 24 runtime.

Changes

Action	Before (node20)	After (node24)
actions/checkout	@v4	@v5
actions/setup-go	@v4	@v6
golangci/golangci-lint-action	@v7	@v9

File touched: .github/workflows/ (single workflow).

• golangci-lint-action@v7 → @v9 (node20 → node24). The repo's .golangci.yml is already v2-format (version: "2") and the step passes no args, so the bump is clean.

Verification

Confirmed via each pinned action.yml (runs.using:):

• checkout@v4 → node20; @v5 → node24
• setup-go@v4 → node20; @v6 → node24
• golangci-lint-action@v7 → node20; @v9 → node24

Diff is version strings only, no other edits.

Runner requirement

The job runs on ubuntu-latest (GitHub-hosted), which already supports the Node 24 runtime — no runner action needed.

Testing

• Run the workflow and confirm checkout / setup-go / golangci-lint run without Node deprecation warnings.