fix: set explicit target-branch for release-please

The default branch is now develop, but release-please should target
main. Without an explicit target-branch, it defaults to the repo's
default branch and never creates a release PR.

Author: tatupesonen

.github/workflows/release-please.yml

@@ -19,6 +19,7 @@ jobs:
       - uses: googleapis/release-please-action@v4
         id: release
         with:
+          target-branch: main
           config-file: release-please-config.json
           manifest-file: .release-please-manifest.json