Handle empty prerelease selection in fetchReleases

Updates fetchReleases.js to write an empty string to selectedPreReleases when no prereleases are found, instead of an empty array. Adjusts selected.json accordingly to maintain consistent data structure.

Author: Stefterv

content/download/selected.json

@@ -5,5 +5,7 @@
     "processing-0270-3.5.4",
     "processing-1310-4.4.10"
   ],
-  "selectedPreReleases": []
+  "selectedPreReleases": [
+    ""
+  ]
 }

scripts/fetchReleases.js

@@ -112,7 +112,7 @@ const fetchReleases = async (githubToken) => {
   );
   const selectedPreReleases = preReleases.length
     ? [preReleases[0].node.tagName]
-    : [];
+    : [""];
   fs.writeFileSync(
     path.join(__dirname, '..', 'content', 'download', 'selected.json'),
     JSON.stringify(