Fix white page issue by reverting to Node 12.x

The site was showing a blank page because Hexo 3.9.0 is incompatible
with Node 20.x. Reverting to Node 12.x which is compatible with the
current Hexo version.

Author: THargreaves

.github/workflows/pages.yml

@@ -13,10 +13,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Use Node.js 20.x
+      - name: Use Node.js 12.x
         uses: actions/setup-node@v4
         with:
-          node-version: '20.x'
+          node-version: '12.x'
       - name: Cache NPM dependencies
         uses: actions/cache@v4
         with: