Fix GitHub action for building production version of master (#13974)

* Update action build to only use external action

.github/workflows/build-master.yml

@@ -7,19 +7,13 @@ on:
 jobs:
   build_master_job:
     runs-on: ubuntu-latest
-    name: Build production version of master to master-built branch
+    name: Build production version of master to master-built branch!
     steps:
       - name: Checkout Jetpack
         uses: actions/checkout@master
-      - name: Build production files
-        run: COMPOSER_MIRROR_PATH_REPOS=1 yarn run build-production
-      - name: Purge dev files
-        run: $GITHUB_WORKSPACE/bin/prepare-built-branch.sh
-      - name: Push to built branch
-        id: commit-and-push
-        uses: automattic/action-commit-to-branch@master
+      - name: Build production version
+        uses: automattic/action-jetpack-build-to-branch@master
         with:
-          branch: 'master-built'
-          commit_message: 'Automated production build from master'
-        env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          branch_pull: 'master'
+          branch_push: 'master-built'
+          commit_message: 'Automated production build from master'