fix: configure action to run one node24

From GitHub,

> Node.js 20 actions are deprecated. The following actions are running
> on Node.js 20 and may not work as expected: freckle/stack-action@v5.
> Actions will be forced to run with Node.js 24 by default starting June
> 2nd, 2026

We've already been using this for the unit suite on CI since Renovate
bumped `.nvmrc` on us and we didn't notice to keep `action.yml` in sync.

Author: pbrisbin

action.yml

@@ -74,5 +74,5 @@ inputs:
     description: |
       **Deprecated** use `env.STACK_YAML` or `stack-arguments` instead.
 runs:
-  using: "node20"
+  using: "node24"
   main: "dist/index.js"