fix: add pnpm install step to create-release-pr workflow (#120)

Lerna requires node_modules/.modules.yaml to parse pnpm lockfile.
Without pnpm install, the workflow fails with:
  Could not find ".modules.yaml" at "/home/runner/work/editor/editor/node_modules/.modules.yaml"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

Author: azu

.github/workflows/create-release-pr.yml

@@ -35,6 +35,9 @@ jobs:
           node-version: 22
           cache: 'pnpm'
 
+      - name: Install dependencies
+        run: pnpm install
+
       - name: Update Version
         run: |
           git config --global user.email "${GIT_AUTHOR_EMAIL}"