Scope release-drafter to master branch releases

Add filter-by-commitish to avoid version confusion between
4.0.x (master) and 3.x (plexus-utils-3.x) releases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gnodet

.github/workflows/release-drafter.yml

@@ -8,5 +8,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: release-drafter/release-drafter@v7
+        with:
+          commitish: master
+          filter-by-commitish: true
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}