Change main_git_branch from master to 1.x

Author: imorland

.github/workflows/frontend.yml

@@ -13,7 +13,7 @@ jobs:
       frontend_directory: ./js
       backend_directory: .
       js_package_manager: yarn
-      main_git_branch: master
+      main_git_branch: 1.x
 
     secrets:
       bundlewatch_github_token: ${{ secrets.BUNDLEWATCH_GITHUB_TOKEN }}