add workflow_dispatch trigger to release-drafter.yml

What changed:
- Added `workflow_dispatch` event to allow manual triggering.

Author: slawekjaranowski

.github/workflows/release-drafter.yml

@@ -3,6 +3,8 @@ on:
   push:
     branches:
       - master
+  workflow_dispatch:
+
 jobs:
   update_release_draft:
     runs-on: ubuntu-latest