fix(ci): release-pr waits for CI to pass before running (#35)

Changed trigger from `on: push` to `on: workflow_run` so release-plz
only creates release PRs after CI completes successfully.

Closes #35

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

Author: crrow

.github/workflows/release-pr.yml

@@ -1,7 +1,9 @@
 name: Release PR
 
 on:
-  push:
+  workflow_run:
+    workflows: [CI]
+    types: [completed]
     branches: [main]
 
 permissions:
@@ -10,6 +12,7 @@ permissions:
 
 jobs:
   release-plz:
+    if: github.event.workflow_run.conclusion == 'success'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4