fix(ci): remove pull_request trigger from Release Drafter workflow

The Release Drafter action was triggered on pull_request events, but when
updating the draft release it used refs/pull/N/merge as target_commitish.
GitHub's API rejects this ephemeral ref, causing:
  'Validation Failed: {"resource":"Release","code":"invalid","field":"target_commitish"}'

The autolabeler feature is not configured in .github/release-drafter.yml,
so the pull_request trigger was not providing any value.

Fix: Only run on push to main, which produces a valid target_commitish.

Author: Ritchie

.github/workflows/release-drafter.yml

@@ -6,11 +6,10 @@ on:
     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:
+  # Removed: pull_request trigger caused "invalid target_commitish" errors
+  # because refs/pull/N/merge is not a valid release commitish.
+  # Re-add if autolabeler is enabled in .github/release-drafter.yml.
+  # pull_request:
   #   types: [opened, reopened, synchronize]
 
 permissions:
@@ -26,16 +25,7 @@ jobs:
       pull-requests: write
     runs-on: ubuntu-latest
     steps:
-      # (Optional) GitHub Enterprise requires GHE_HOST variable set
-      #- name: Set GHE_HOST
-      #  run: |
-      #    echo "GHE_HOST=${GITHUB_SERVER_URL##https:\/\/}" >> $GITHUB_ENV
-
-      # Drafts your next Release notes as Pull Requests are merged into "master"
+      # Drafts your next Release notes as Pull Requests are merged into "main"
       - uses: release-drafter/release-drafter@v7
-        # (Optional) specify config name to use, relative to .github/. Default: release-drafter.yml
-        # with:
-        #   config-name: my-config.yml
-        #   disable-autolabeler: true
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}