ci: docs should build from v0.3

.github/workflows/api_doc_build.yml

@@ -27,6 +27,7 @@ jobs:
     steps:
       - uses: actions/checkout@v5
         with:
+          ref: v0.3
           path: langchain
       - uses: actions/checkout@v5
         with:

.github/workflows/check_new_docs.yml

@@ -5,7 +5,7 @@ name: '📑 Integration Docs Lint'
 
 on:
   push:
-    branches: [master]
+    branches: [v0.3]
   pull_request:
 
 # If another push to the same PR or branch happens while this workflow is still running,