Change source of truth for node version in github to package.json, so…

… see if that makes it fetch the right yarn version as defined there.

.github/workflows/ruby.yml

@@ -44,7 +44,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v4
         with:
-          node-version-file: '.nvmrc'
+          node-version-file: 'package.json'
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1