Force Node 24 for JS actions in CI

Opt into Node 24 ahead of the June 2026 runner default so
transitively-invoked github-script steps stop emitting the
Node 20 deprecation warning.

Author: emazzotta

.github/workflows/build.yml

@@ -9,6 +9,7 @@ on:
 env:
   TAG_PREFIX: emazzotta/lighthouse-badges
   BUN_VERSION: 1.3.12
+  FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
 
 permissions:
   id-token: write