build(deps): bump actions/checkout from 4 to 6

Author: merger-application[bot]

.github/workflows/diagram.yml

@@ -12,7 +12,7 @@ jobs:
       contents: write
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Mermaid CLI
         run: npm install -g @mermaid-js/mermaid-cli