fix upm branch name from upm-2.0 to upm-2

Author: endel

.github/workflows/unity-upm-release.yml

@@ -163,7 +163,7 @@ jobs:
         uses: s0/git-publish-subdir-action@develop
         env:
           REPO: self
-          BRANCH: upm-2.0
+          BRANCH: upm-2
           FOLDER: upm-package/
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}