Update lib/mdx/getFiles to only return files with mdx extension.

lib/mdx.js

@@ -26,8 +26,12 @@ const root = process.cwd()
 export function getFiles(type) {
   const prefixPaths = path.join(root, 'data', type)
   const files = getAllFilesRecursively(prefixPaths)
+
+  // Filter to include only files with .mdx extension
+  const mdxFiles = files.filter(file => file.endsWith('.mdx'));
+
   // Only want to return workshop/path and ignore root, replace is needed to work on Windows
-  return files.map((file) => file.slice(prefixPaths.length + 1).replace(/\\/g, '/'));
+  return mdxFiles.map((file) => file.slice(prefixPaths.length + 1).replace(/\\/g, '/'));
 }
 
 export function formatSlug(slug) {