fix: remove explicit pnpm version to resolve version conflict

Remove explicit version specification from pnpm/action-setup to avoid
conflicts with the packageManager field in package.json. This allows
the action to automatically use the repository's specified pnpm version.

Fixes: Error: Multiple versions of pnpm specified (ERR_PNPM_BAD_PM_VERSION)

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

Co-Authored-By: Claude <[email protected]>

Author: ScriptedAlchemy

.github/workflows/on-pull-request.yml

@@ -138,7 +138,6 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: 9
           run_install: false
 
       - name: Setup Node.js with caching

.github/workflows/on-push.yml

@@ -65,7 +65,6 @@ jobs:
       - name: Setup pnpm
         uses: pnpm/action-setup@v4
         with:
-          version: 9
           run_install: false
 
       - name: Setup Node.js with caching