Add base branch to PR creation

Author: bigfluffycookie

.github/workflows/sync-ai-models.yml

@@ -57,6 +57,7 @@ jobs:
         uses: peter-evans/create-pull-request@v7
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
+          base: main
           commit-message: 'Update AI provider models from models.dev'
           title: 'Update AI Provider Models'
           body: |