[ci] Standardize node version and timezones

Quick change to standardize on a single timezone across all workflows
and to use the same version of node (18.20.1).

Also updates .nvmrc

ghstack-source-id: e1d43006ec
Pull Request resolved: https://github.com/facebook/react/pull/30323

.github/workflows/runtime_commit_artifacts.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches: [main, meta-www, meta-fbsource]
 
+env:
+  TZ: /usr/share/zoneinfo/America/Los_Angeles
+
 jobs:
   download_artifacts:
     runs-on: ubuntu-latest