Remove explicit pnpm version from workflows; use packageManager field

pnpm/action-setup@v4 reads the version from packageManager in package.json.
Removing the hardcoded version: 9 eliminates the conflict with pnpm@10.30.0.

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

Author: ctrimm

.github/workflows/co2-emissions-cron.yml

@@ -14,8 +14,6 @@ jobs:
 
       - name: Install pnpm
         uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - name: Setup Node.js
         uses: actions/setup-node@v4

.github/workflows/deploy.yml

@@ -34,8 +34,6 @@ jobs:
 
       - name: Install pnpm
         uses: pnpm/action-setup@v4
-        with:
-          version: 9
 
       - name: Setup Node.js
         uses: actions/setup-node@v4