build: fix file extension for github action (#47976)

Fix the file extension for the new assistant-to-the-branch-mananager action

PR Close #47976

.github/workflows/assistant-to-the-branch-manager.yml

@@ -0,0 +1,22 @@
+name: DevInfra
+
+on:
+  push:
+  pull_request_target:
+    types: [opened, synchronize, reopened, ready_for_review]
+
+# Declare default permissions as read only.
+permissions:
+  contents: read
+
+jobs:
+  assistant_to_the_branch_manager:
+    if: github.action == 'pull_request_target' or github.action == 'push'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@2541b1294d2704b0964813337f33b291d3f8596b # tag=v3.0.2
+        with:
+          persist-credentials: false
+      - uses: angular/dev-infra/github-actions/branch-manager@aa4dcc8fa853e6b5f3345e6f1bac5255c7d7a871
+        with:
+          angular-robot-key: ${{ secrets.ANGULAR_ROBOT_PRIVATE_KEY }}