Update release-drafter.yml to add PR events for autolabeler (#41)

Author: shenxianpeng

.github/workflows/release-drafter.yml

@@ -4,6 +4,13 @@ on:
   push:
     branches:
       - "main"
+  # pull_request event is required only for autolabeler
+  pull_request:
+    # Only following types are handled by the action, but one can default to all as well
+    types: [opened, reopened, synchronize]
+  # pull_request_target event is required for autolabeler to support PRs from forks
+  pull_request_target:
+    types: [opened, reopened, synchronize]
   workflow_dispatch:
 
 jobs: