fix: search index upload (supabase#32904)

Search index pipeline shouldn't be trying to read troubleshooting section yet (those are still searched via GH discussions). Trying to read it errors as they don't have the same frontmatter shape as other guides content.

Author: charislam

apps/docs/scripts/search/sources/index.ts

@@ -1,3 +1,4 @@
+import { sep } from 'node:path'
 import {
   GitHubDiscussionLoader,
   type GitHubDiscussionSource,
@@ -93,9 +94,13 @@ export async function fetchSources() {
     'spec/common-cli-sections.json'
   ).load()
 
-  const guideSources = (await walk('content'))
-    .filter(({ path }) => /\.mdx?$/.test(path))
-    .filter(({ path }) => !ignoredFiles.includes(path))
+  const guideSources = (await walk('content/guides'))
+    .filter(
+      ({ path }) =>
+        /\.mdx?$/.test(path) &&
+        !ignoredFiles.includes(path) &&
+        !path.split(sep).some((part) => part.startsWith('_'))
+    )
     .map((entry) => new MarkdownLoader('guide', entry.path, { yaml: true }).load())
 
   const partnerIntegrationSources = (await fetchPartners()).map((partner) =>