fix(ci): remove pull_request trigger from release-drafter workflow

The release-drafter action fails when triggered on pull_request events
because it attempts to update the draft release with target_commitish
set to refs/pull/XXX/merge, which GitHub's API rejects with:

  Validation Failed: {resource:Release, code:invalid, field:target_commitish}

The pull_request trigger is only needed for the autolabeler feature,
which is not configured in this repo. Removing it so the workflow only
runs on push to main, which is the correct and intended behavior.

Fixes recurring failures on runs: 23369773059, 23369768998, 23111592904

Author: Ritchie

.github/workflows/release-drafter.yml

@@ -2,16 +2,12 @@ name: Release Drafter
 
 on:
   push:
-    # branches to consider in the event; optional, defaults to all
+    # Only draft releases when pushing to main
     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]
+  # pull_request trigger removed: causes "invalid target_commitish" error
+  # when release-drafter tries to update draft release with refs/pull/XXX/merge.
+  # Autolabeler is not in use here, so the pull_request trigger is unnecessary.
 
 permissions:
   contents: read
@@ -26,12 +22,7 @@ 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: