ci: pin publish workflow to minimum supported Node version

The publish workflow should use Node 22 (the minimum supported version
per engines.node >=22.0.0) to ensure maximum compatibility for all
users. The CI matrix already validates both Node 22 and 24.

Also adds a Renovate package rule to prevent automated bumps of the
Node version in the publish workflow.

Refs #106

Author: iamfj

.github/workflows/publish.yml

@@ -47,7 +47,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v6
         with:
-          node-version: "22"
+          node-version: "22" # Pin to minimum supported version for publishing
           registry-url: "https://registry.npmjs.org"
 
       - name: Clean install

renovate.json

@@ -26,6 +26,13 @@
       "description": "Group GitHub Actions updates",
       "matchManagers": ["github-actions"],
       "groupName": "github actions"
+    },
+    {
+      "description": "Pin publish workflow to minimum supported Node version",
+      "matchManagers": ["github-actions"],
+      "matchPackageNames": ["node"],
+      "matchFileNames": [".github/workflows/publish.yml"],
+      "enabled": false
     }
   ]
 }